Cherenkov light detection circuit and detector

Abstract

The invention provides a Cerenkov optical detection circuit and a detector, which are used for gamma ray imaging, and comprise a Cerenkov emission material configured to receive gamma photons and excite to generate optical signals; the photoelectric detector is in coupling connection with the Cherenkov emission material and is configured to receive the optical signal and convert the optical signal into an electric signal; the first broadband radio frequency amplifier is connected with the output end of the photoelectric detector and is used for receiving the electric signal and primarily amplifying the electric signal to form an amplified signal; and the second broadband radio frequency amplifier is connected with the output end of the first broadband radio frequency amplifier and is used for carrying out secondary amplification on the amplified signal to form a time signal. Compared with the prior art, the Cherenkov optical detection circuit adopts the two-stage low-power-consumption broadband radio-frequency amplifier to read out the time signal and does not use a balun transformer structure any more, so that the signal transmission path can be optimized, the system integration degree can be improved, the power consumption can be reduced, the structure is simple, and the cost is low. And the Cerenkov radiation light can be detected so as to improve the time resolution of the photoelectric detector.

Description

Technical Field

[0001] The present invention relates to a Cherenkov light detection circuit and a detector, belonging to the field of gamma-ray imaging. Background Art

[0002] The phenomenon of Cherenkov radiation was first discovered by Russian physicist Pavel Cherenkov in 1934, and he was awarded the Nobel Prize in Physics in 1958 for this discovery. When a charged particle (such as an electron) travels through a medium at a speed greater than the speed of light in that medium, Cherenkov radiation occurs in the medium. The wavelength range of this light is usually between ultraviolet and visible light, and the radiation angle is closely related to the speed of the particle and the refractive index of the medium.

[0003] In a positron emission tomography (PET) detector, after 511 keV gamma photons interact with a high-refractive-index scintillation crystal (such as bismuth germanate BGO), mainly scintillation light is generated, and high-speed electrons may also be generated. The movement of these electrons in the crystal medium will excite Cherenkov light. With the development of optical detector technology and fast electronics technology in recent years, the time resolution of PET detectors has become higher and higher. Time resolution is crucial for PET imaging quality. A better time resolution can improve the image signal-to-noise ratio, and through time-of-flight (TOF) technology, the time resolution of PET can be greatly improved. Compared with traditional scintillation light, since the scintillation light amplitude of BGO crystals is relatively small (generally less than 100 mV) and the scintillation light decay time is relatively long (the decay time constant is 300 ns), the obtained time resolution is generally above 5 ns and cannot be used for TOF-PET detectors. However, Cherenkov light can be used to more accurately estimate the arrival time of gamma photons, thereby improving the coincidence time resolution (CTR). Due to its ultrafast response characteristics, enhancement effect in a high-refractive-index medium, and complementarity with scintillation light, Cherenkov light has become an important research direction for improving the time resolution of PET systems.

[0004] Existing Cherenkov light detection circuits use high-gain low-noise amplifiers with a bandwidth exceeding 1 GHz to ensure a fast response to Cherenkov light. In these high-frequency circuit designs, a common method is to adopt a structure of a balun transformer followed by an amplifier in the reading path of the time signal. However, this solution has the following defects: First, balun transformers are usually relatively large in size (2×2 mm 2), which makes it difficult to miniaturize the detector system and limits its use in application scenarios that require a compact design. Secondly, the balun transformer contains magnetic materials inside. If it is used in a device that combines PET and MRI, it may interfere with the magnetic field uniformity and affect the imaging quality of MRI. In addition, the amplifiers used in such circuits consume a large amount of power (usually the power consumption of a single operational amplifier is above 200 mW). When applied in a large-scale detection system, problems related to power consumption and heat dissipation will occur, thus affecting the long-term stable operation of the system.

[0005] In view of this, it is necessary to improve the existing Cherenkov light detection circuit to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide an improved Cherenkov light detection circuit and a detector using this circuit. The Cherenkov light detection circuit uses two-stage low-power broadband RF amplifiers for time signal readout and no longer uses the balun transformer structure, thereby optimizing the signal transmission path, improving the system integration, reducing power consumption, having a simple structure, and being able to detect Cherenkov radiation light to improve the time resolution of the photodetector.

[0007] To achieve the above purpose, in a first aspect, the present invention provides a Cherenkov light detection circuit for gamma-ray imaging, including:

[0008] A Cherenkov emission material configured to receive gamma photons and generate an optical signal by excitation;

[0009] A photodetector coupled to the Cherenkov emission material and configured to receive the optical signal and convert the optical signal into an electrical signal;

[0010] A first broadband RF amplifier connected to the output end of the photodetector, configured to receive the electrical signal and preliminarily amplify the electrical signal to form an amplified signal;

[0011] A second broadband RF amplifier connected to the output end of the first broadband RF amplifier, configured to perform secondary amplification on the amplified signal output by the first broadband RF amplifier to form a time signal.

[0012] As a further improvement of the present invention, the Cherenkov emission material includes a scintillation crystal and a pure Cherenkov emission material.

[0013] As a further improvement of the present invention, the optical signal generated by excitation of the Cherenkov emission material includes Cherenkov radiation light and scintillation light.

[0014] As a further improvement of the present invention, both the first broadband RF amplifier and the second broadband RF amplifier operate in an open-loop state.

[0015] As a further improvement of the present invention, the photodetector is provided with a first output terminal and a second output terminal. The first broadband radio frequency amplifier is connected to the first output terminal, and a filtering capacitor is connected to the second output terminal to filter out the DC signal in the electrical signal and form an energy signal.

[0016] As a further improvement of the present invention, a first capacitor is connected between the first output terminal and the input terminal of the first broadband radio frequency amplifier. The first capacitor is configured to filter out the DC signal in the electrical signal in an AC coupling manner.

[0017] As a further improvement of the present invention, a second capacitor is connected between the output terminal of the first broadband radio frequency amplifier and the input terminal of the second broadband radio frequency amplifier. The second capacitor is configured to filter out the DC signal in the amplified signal in an AC coupling manner.

[0018] As a further improvement of the present invention, a high-frequency optimization capacitor is connected to the output terminal of the second broadband radio frequency amplifier to compensate for high-frequency attenuation.

[0019] As a further improvement of the present invention, the Cherenkov light detection circuit further includes a connector connected to the output terminal of the second broadband radio frequency amplifier, and the time signal is output through the connector.

[0020] As a further improvement of the present invention, the effective light detection area of the photodetector matches the scintillation crystal, and the photodetector is coupled to the scintillation crystal in a one-to-one manner.

[0021] As a further improvement of the present invention, the scintillation crystal is one of lutetium yttrium silicate crystal, lutetium silicate crystal, bismuth germanate crystal, lanthanum bromide crystal, gadolinium silicate crystal, and gadolinium lutetium silicate crystal.

[0022] In a second aspect, the present invention also provides a detector, including the Cherenkov light detection circuit described in the first aspect. In some embodiments, the detector may be a positron emission tomography (PET) detector.

[0023] The beneficial effects of the present invention are as follows: The Cherenkov light detection circuit of the present invention uses two-stage low-power broadband radio frequency amplifiers for time signal reading and no longer uses a balun transformer structure, thereby optimizing the signal transmission path, improving system integration, reducing power consumption, having a simple structure, and being able to detect Cherenkov radiation light to improve the time resolution of the photodetector. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a circuit diagram of the Cherenkov light detection circuit of the present invention.

[0025] Figure 2 is the output signal when the LYSO crystal is applied to Figure 1 the Cherenkov light detection circuit shown.

[0026] Figure 3 is the time resolution when the LYSO crystal is applied to Figure 1 the Cherenkov light detection circuit shown.

[0027] Figure 4 is the output signal when the BGO crystal is applied to Figure 1 the Cherenkov light detection circuit shown.

[0028] Figure 5 is the time resolution when the BGO crystal is applied to Figure 1 the Cherenkov light detection circuit shown. Detailed implementation manner

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] As Figure 1 shown, the present invention discloses a Cherenkov light detection circuit for gamma-ray imaging. The key lies in improving and optimizing the signal path, including a Cherenkov emission material, a photodetector, and two-stage low-power broadband RF amplifiers.

[0031] Among them, the Cherenkov emission material is configured to be able to receive gamma photons and excite to generate an optical signal; the photodetector is coupled to the Cherenkov emission material and is configured to receive the optical signal and convert the optical signal into an electrical signal. The Cherenkov emission material includes a scintillation crystal and a pure Cherenkov emission material (such as lead glass, lead fluoride PbF2, thallium chloride TICI, thallium bromide TIBr, etc.). In this embodiment, the Cherenkov emission material is preferably a scintillation crystal. The optical signal generated after the scintillation crystal receives gamma photons includes Cherenkov radiation light and scintillation light. The scintillation crystal is preferably one of lutetium yttrium silicate crystal (LYSO), lutetium silicate crystal (LSO), bismuth germanate crystal (BGO), lanthanum bromide crystal (LaBr3), gadolinium silicate crystal (GSO), lutetium gadolinium silicate crystal (LGSO), but should not be limited thereto.

[0032] Before the scintillation crystal is coupled with the photodetector, the six faces of the scintillation crystal can be polished to reduce light scattering and absorption and improve the light transmission efficiency. In addition, four side faces of the scintillation crystal and the gamma-ray incident face can be covered with high-reflectivity materials, including but not limited to barium sulfate, enhanced specular reflector (ESR), titanium dioxide, etc., and the reflectivity requirement is greater than 90%. Preferably, the high-reflectivity material is selected as the ESR material, so that the scintillation light can be reflected to the greatest extent, the light utilization rate can be enhanced, and the detection efficiency can be further improved.

[0033] The effective light detection area of the photodetector matches the scintillation crystal, which can ensure efficient light collection. The photodetector is coupled to the scintillation crystal one-to-one, which can reduce the influence of light loss and coupling non-uniformity on the time resolution.

[0034] In this embodiment, the photodetector preferably uses an MRI-compatible silicon photomultiplier (SiPM) because: the SiPM has high sensitivity and can efficiently detect the signals of Cherenkov radiation light and scintillation light. Optionally, Figure 1 the specific model of the SiPM used is AFBR-S4N33CO13 of Broadcom Corporation in the United States, which enhances the detection efficiency of near-ultraviolet light (NUV). Of course, in other embodiments, the SiPM model can also be from Sensl in Ireland, Hamamatsu in Japan, KETEK in Germany, FBK in Italy, Cremat in Spain, AdvanSiD in Italy, and Zecotek Photonics in Canada, which is not limited here.

[0035] As Figure 1 shown, after the optical signal enters the photodetector SiPM, it undergoes photoelectric conversion inside the photodetector SiPM and is output from the cathode end, and successively passes through two-stage low-power broadband radio frequency amplifiers. Both of these two-stage low-power broadband radio frequency amplifiers operate in an open-loop state without adding a negative feedback circuit, so that the effective amplification and transmission of high-frequency time signals can be ensured, and at the same time, the volume limitation and magnetic material interference brought by the traditional balun transformer structure can be avoided.

[0036] Specifically, the two - stage low - power broadband RF amplifiers are the first broadband RF amplifier 10 and the second broadband RF amplifier 20 respectively. Among them, the first broadband RF amplifier 10 is connected to the output terminal (i.e., the cathode terminal) of the photodetector SiPM, and is used to receive the electrical signal formed after photoelectric conversion and preliminarily amplify the electrical signal to form an amplified signal. The second broadband RF amplifier 20 is connected to the output terminal of the first broadband RF amplifier 10, and is used to perform secondary amplification on the amplified signal output by the first broadband RF amplifier 10. At this time, electrical signals with very fast pulse rise can be collected as time signals. That is to say, the first broadband RF amplifier 10 mainly performs broadband amplification on the initial electrical signal output by the photodetector SiPM to ensure that the electrical signal can enter the subsequent circuit with a sufficiently high signal - to - noise ratio (SNR); the main function of the second broadband RF amplifier 20 is to further enhance the amplitude of the time signal and optimize the rise time of the signal to improve the time resolution.

[0037] Since the requirements for signal quality in time measurement are extremely high, both the first broadband RF amplifier 10 and the second broadband RF amplifier 20 operate in an open - loop state without adding a negative feedback circuit to enhance the signal strength.

[0038] To reduce the influence of low - frequency noise and DC drift, serial capacitive AC coupling is used before and after the first broadband RF amplifier 10 to remove the DC component, so as to improve the stability of signal transmission. Specifically, the photodetector SiPM is provided with a first output terminal and a second output terminal. The first broadband RF amplifier 10 is connected to the first output terminal, and a first capacitor 11 is connected between the first output terminal and the input terminal of the first broadband RF amplifier 10. The first capacitor 11 can filter out the DC signal in the electrical signal in an AC - coupling manner; a second capacitor 12 is connected between the output terminal of the first broadband RF amplifier 10 and the input terminal of the second broadband RF amplifier 20. The second capacitor 12 can filter out the DC signal in the amplified signal in an AC - coupling manner. After filtering the DC signal twice, the electrical signal entering the second broadband RF amplifier 20 can be transmitted more stably.

[0039] In addition, to suppress the attenuation of high - frequency signals and improve the clarity of time signals, a high - frequency optimization capacitor 13 is also connected to the output terminal of the second broadband RF amplifier 20 to compensate for high - frequency attenuation, so that the output signal has a faster rise time, so as to read the time signal from the output terminal of the second broadband RF amplifier 20. To facilitate reading the time signal, the Cherenkov light detection circuit further includes a first connector 21 connected to the output terminal of the second broadband RF amplifier 20. Thus, the time signal can be output through the first connector 21 to an external time readout and processing system for subsequent processing. Preferably, the first connector 21 is an SMA connector, which can isolate external noise signals.

[0040] A filter capacitor 14 is connected to the second output terminal of the photodetector SiPM. This filter capacitor 14 can filter out the DC signal in the electrical signal, so that slower scintillation light signals can be collected as energy signals. This energy signal is mainly used to create an energy window (400 keV - 600 keV) to eliminate the signals of Compton scattering events. To facilitate reading the energy signal, the Cherenkov light detection circuit also includes a second connector 22 connected to the second output terminal of the photodetector SiPM, so that the energy signal can be output to an external host computer through the second connector 22 for subsequent processing. Preferably, the second connector 22 is also an SMA connector, which can isolate external noise signals.

[0041] In practical applications, when gamma photons enter the scintillation crystal, Cherenkov radiation light and scintillation light will be excited and generated; these light signals are detected by the photodetector SiPM and converted into electrical signals; then, the electrical signals are first preliminarily amplified by the first broadband RF amplifier 10, and then transmitted through AC coupling to the second broadband RF amplifier 20 for further amplification; finally, the signal amplified by the second broadband RF amplifier 20 is used as a time signal and output to the subsequent time readout and processing system for accurately measuring the arrival time of gamma photons, thereby improving the time resolution of the photodetector SiPM; at the same time, the energy signal is directly read from the second output terminal of the photodetector SiPM without adding an additional operational amplifier. This not only simplifies the circuit design, reduces costs, but also reduces the complexity of signal processing and potential noise sources.

[0042] Of course, to ensure the normal operation of the photodetector SiPM and the two - stage low - power broadband RF amplifiers, the Cherenkov light detection circuit of the present invention also includes a first control circuit connected to the photodetector SiPM and a second control circuit connected to the first broadband RF amplifier 10 and the second broadband RF amplifier 20 respectively. Among them, the first control circuit consists of two series - connected voltage - dividing resistors R1, R2 and a filter capacitor C1 connected between the two voltage - dividing resistors R1, R2 and grounded. When the external power supply provides a bias voltage for the photodetector SiPM, the filter capacitor C1 can filter out the AC signal in the bias voltage, ensuring that only the DC signal flows through the voltage - dividing resistors R1, R2 to supply power to the photodetector SiPM, making the photodetector SiPM in a breakdown state and ensuring that the photodetector SiPM can operate normally.

[0043] The second control circuit consists of three filter capacitors C2, C3, and C4. When the external power supply provides a bias voltage for the two-stage low-power broadband RF amplifier, the filter capacitor C2 first filters out the AC signal in the bias voltage, allowing the DC signal to flow into the first broadband RF amplifier 10 and the second broadband RF amplifier 20. Before the DC signal flows into the first broadband RF amplifier 10 and the second broadband RF amplifier 20, the filter capacitors C3 and C4 are respectively used to filter the DC signal again to filter out the remaining AC signal in the DC signal, ensuring that only the DC signal flows into the first broadband RF amplifier 10 and the second broadband RF amplifier 20 to supply power to the first broadband RF amplifier 10 and the second broadband RF amplifier 20.

[0044] To verify the feasibility of the Cherenkov light detection circuit of the present invention, the following will be described by taking 2 specific embodiments as examples, but it should not be limited thereto.

[0045] Embodiment 1:

[0046] Use a detector structure of a pair of 3×3×3mm 3 LYSO single crystal bars are respectively coupled one-to-one on SiPMs (model AFBR-S4N33CO13 of Broadcom, USA) that enhance the detection efficiency of near-ultraviolet light (NUV). Both two-stage low-power broadband RF amplifiers are selected as NXP BGA2851 (power consumption is 35mW), and the energy signal and time signal are both output through SMA connectors. As Figure 2 and Figure 3 shown, Figure 2 the green and red curves in Figure 2 are the energy signals extracted after the detector structure outputs from the cathode of the SiPM. It can be seen that: the energy signal has a large amplitude (the highest value is about 580mV), is slow (the pulse duration is about 300ns), is convenient to be extracted by ordinary electronics, and the Compton scattering events can be eliminated by using an energy window (400keV - 600keV); while Figure 3 the blue and orange curves in

[0047] are the time signals extracted after passing through the two-stage low-power broadband RF amplifier. It can be seen that: the time signal has a large amplitude (the highest value is 500mV), and is very fast (the pulse rise time is about 0.8ns). Then, a 10GHz sampling rate oscilloscope (model DS7000 of RIGOL) can be used to extract 4 channels of signals, and the data is screened through calculation and the energy window. The time resolution is 138.4ps, and the specific reference is Figure 3 .

[0047] Embodiment 2:

[0048] Use a detector structure of a pair of 3×3×3mm 3The BGO single crystal bars are coupled one-to-one to SiPMs (Broadcom AFBR-S4N33CO13 model in the United States) that enhance the detection efficiency of near-ultraviolet light (NUV). Both two-stage low-power broadband RF amplifiers are selected as NXP BGA2851 (with a power consumption of 35 mW), and both the energy signal and the time signal are output through SMA connectors. As Figure 4 and Figure 5 shown, Figure 4 the green and red curves in Figure 4 are the energy signals extracted after the detector structure outputs from the SiPM cathode. It can be seen that: the energy signal has a small amplitude (the maximum value is close to 100 mV) and is slow (the pulse duration is about 900 ns), which is convenient for extraction by ordinary electronics, and the energy window (400 keV - 600 keV) is used to eliminate Compton scattering events; while Figure 5 the blue and orange curves in

[0049] are the time signals extracted after passing through two-stage low-power broadband RF amplifiers. It can be seen that: the time signal has a large amplitude (the maximum value is about 480 mV) and is very fast (the pulse rise time is 2 ns). After that, a 10 GHz sampling rate oscilloscope (Rigol DS7000 model) can be used to extract 4 channels of signals, and the data is screened through calculation and the energy window. The time resolution is 539 ps, and the specific parameters are 2 2 .In Embodiments 1 and 2, the effective light detection area of the SiPM is 3×3 mm

[0050] , which can be tightly coupled one-to-one with the scintillation crystal to ensure maximum collection of light signals from the scintillation crystal. One signal output from the cathode end of the SiPM is connected to the input end of the first broadband RF amplifier 10. Of course, in other embodiments, the effective light detection area of the SiPM can also be set to 6×6, 4×4, 2×2 or 1×1 mm

[0051] This is not limited here.

[0052] 1. By removing the balun transformer structure in the traditional circuit, the circuit volume and cost are reduced, which is convenient for multi-channel integration of the later PET system, and the circuit can be used in the design combined with MRI, expanding the application scope.

[0053] 2. A two-stage low-power wideband RF amplifier is adopted. On the basis of reducing the power consumption of the circuit, it can also improve the time resolution by reading out the Cherenkov radiation light, which is beneficial to heat dissipation management and service life in large-scale circuit design.

[0054] 3. Traditional Cherenkov light detection circuits usually use an additional operational amplifier to read the energy signal, while the present invention directly reads the energy signal at the cathode end of the SiPM, removing the additional amplifier, further simplifying the circuit design and reducing costs.

[0055] In addition, the present invention also provides a detector, which includes the above-mentioned Cherenkov light detection circuit. In some embodiments, the detector may be a positron emission tomography (PET) detector. However, it should not be limited thereto.

[0056] In summary, the Cherenkov light detection circuit of the present invention uses a two-stage low-power wideband RF amplifier to read out the time signal, and no longer uses the balun transformer structure, thereby optimizing the signal transmission path, improving the system integration, reducing the power consumption, having a simple structure, and being able to detect the Cherenkov radiation light to improve the time resolution of the photodetector.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A Cherenkov light detection circuit for gamma-ray imaging, characterized in that, Comprising: A Cherenkov emission material configured to receive gamma photons and excite the generation of an optical signal; A photodetector coupled to the Cherenkov emission material and configured to receive the optical signal and convert the optical signal into an electrical signal; A first broadband radio frequency amplifier connected to the output terminal of the photodetector for receiving the electrical signal and preliminarily amplifying the electrical signal to form an amplified signal; A second broadband radio frequency amplifier connected to the output terminal of the first broadband radio frequency amplifier for secondarily amplifying the amplified signal output by the first broadband radio frequency amplifier to form a time signal.

2. The Cerenkov light detection circuit according to claim 1, wherein: The Cherenkov emission material includes a scintillation crystal and a pure Cherenkov emission material.

3. The Cerenkov light detection circuit according to claim 1, wherein: The optical signal generated by exciting the Cherenkov emission material includes Cherenkov radiation light and scintillation light.

4. The Cerenkov light detection circuit according to claim 1, wherein: Both the first broadband radio frequency amplifier and the second broadband radio frequency amplifier operate in an open-loop state.

5. The Cerenkov light detection circuit according to claim 1, wherein: The photodetector is provided with a first output terminal and a second output terminal. The first broadband radio frequency amplifier is connected to the first output terminal, and the second output terminal is connected with a filter capacitor to filter out the DC signal in the electrical signal to form an energy signal.

6. The Cerenkov light detection circuit according to claim 5, characterized in that: A first capacitor is connected between the first output terminal and the input terminal of the first broadband radio frequency amplifier. The first capacitor is configured to filter out the DC signal in the electrical signal in an AC coupling manner.

7. The Cerenkov light detection circuit according to claim 6, characterized in that: A second capacitor is connected between the output terminal of the first broadband radio frequency amplifier and the input terminal of the second broadband radio frequency amplifier. The second capacitor is configured to filter out the DC signal in the amplified signal in an AC coupling manner.

8. The Cerenkov light detection circuit according to claim 1, wherein: The output terminal of the second broadband radio frequency amplifier is connected with a high-frequency optimization capacitor to compensate for high-frequency attenuation.

9. The Cerenkov light detection circuit according to claim 1, characterized in that: The Cherenkov light detection circuit further includes a connector connected to the output terminal of the second broadband radio frequency amplifier, and the time signal is output through the connector.

10. A detector, characterized in that: Including the Cherenkov light detection circuit according to any one of claims 1 to 9.

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