CN114235875A - A closed-loop detection system for low-field nuclear magnetic resonance Larmor frequencies - Google Patents

Abstract

The invention discloses a closed loop detection system of low-field nuclear magnetic resonance Larmor frequency, which comprises an embedded microprocessor, a radio frequency signal generator, a radio frequency power amplification circuit, a radio frequency switch circuit and a low-noise preamplification circuit, wherein when Larmor frequency detection is carried out, the influence of factors such as detection environment, magnet processing precision, magnet structure design error and the like on the magnetic field strength is considered, the magnetic field strength range is determined in advance, then a corresponding frequency sweep frequency range is determined based on the magnetic field strength range, periodic frequency sweep is carried out in the frequency sweep frequency range to obtain digital enveloper signals corresponding to all frequency sweep frequencies, and finally the frequency sweep frequency bound by the digital enveloping signals with the maximum signal amplitude is taken as the detected Larmor frequency; the method has the advantages that the detection result is not influenced by factors such as the detection environment, the magnet machining precision and the magnet structure design error, and the Larmor frequency detection precision is high.

Description

Closed-loop detection system for low-field nuclear magnetic resonance Larmor frequency

Technical Field

The invention relates to a detection system of low-field nuclear magnetic resonance Larmor frequency, in particular to a closed-loop detection system of low-field nuclear magnetic resonance Larmor frequency.

Background

The nuclear magnetic resonance detection technology is widely appliedThe method is used for detection technologies in the fields of biomedicine, nondestructive detection, petroleum exploration and the like. The technology utilizes the interaction between atomic magnetism and an external magnetic field to detect and analyze different generated nuclear magnetic resonance signals, thereby determining the substance to be detected. Due to being in the main magnetic field B₀In the detection substance has numerous protons moving in the main magnetic field B₀Will cancel each other out, while the components of the magnetic moment in the Z direction add up to form a longitudinal magnetization vector that cannot pass perpendicular to the main magnetic field B₀The radio frequency coil of the direction measures directly. When in the direction perpendicular to the main magnetic field B₀After a radio frequency pulse is applied to the radio frequency coil in the direction, the protons in the thermal equilibrium state absorb the radio frequency pulse energy to generate energy level transition, meanwhile, the radio frequency pulse energy pushes the protons to the synchronous state and spins together with the protons, then the protons generate spin signals with Larmor frequency as precession frequency, transverse magnetization is generated at the moment, and the transverse magnetization can be detected by the radio frequency coil. Based on the theory of electromagnetic field, when the frequency w of radio frequency signal and the main magnetic field B₀When the Larmor frequencies of protons in the detection substance are the same, a nuclear magnetic resonance phenomenon occurs. If the frequency w of the radio frequency signal and the main magnetic field B₀When the Larmor frequencies of protons in the detected substance are inconsistent, most of the protons in the detected substance cannot generate resonance signals, so that echo signals received by the coil are greatly attenuated, and the detection result is inaccurate.

At present, in the practical application of low-field nuclear magnetic resonance, the requirements on the magnetic field intensity and the magnetic field uniformity are higher, however, the magnetic field intensity and the magnetic field uniformity of a magnet are influenced by the detection environment, the magnet processing technology, the magnet structure design error and the like, and the magnetic field intensity and the magnetic field uniformity influence the Larmor frequency of protons. Traditionally, the intensity of the magnetic field is measured by a gauss meter, and randomness and inaccuracy exist in the mode of obtaining the Larmor frequency by the Larmor equation. Therefore, how to eliminate the above immittability factors and accurately determine the Larmor frequency of the nuclear magnetic resonance has important significance for the application of low-field nuclear magnetic resonance.

A small NMR biomolecular sensor is disclosed in the literature (Nan Sun, Yong Liu, Ling Qin, Hakho Lee, Ralph weisslelel, donhe ham. small NMR biomolecular sensors, university of texas, austin division, 2013.) that calculates the Larmor frequency required for NMR to occur in the sensor by measuring the magnitude of the magnetic field strength of the main magnetic field and combining the Larmor equation. However, when the sensor measures the magnetic field intensity of the main magnetic field, the magnetic field intensity errors caused by the detection environment, the precision of a magnetic field intensity measuring instrument and the like are not considered, and the accuracy of the magnetic field intensity of the main magnetic field directly influences the Larmor frequency of nuclear magnetic resonance calculated by the following sensor through a Larmor equation, so that the final detection precision is not high.

Disclosure of Invention

The invention aims to solve the technical problem of providing a low-field nuclear magnetic resonance Larmor frequency closed-loop detection system which is not influenced by factors such as a detection environment, magnet machining precision, magnet structure design errors and the like and has higher Larmor frequency detection precision.

The technical scheme adopted by the invention for solving the technical problems is as follows: a closed loop detection system of low-field nuclear magnetic resonance Larmor frequency comprises an embedded microprocessor, a radio frequency signal generator, a radio frequency power amplification circuit, a radio frequency switch circuit, a low-noise preamplification circuit, a heterodyne locking amplification circuit and an analog-to-digital conversion circuit; the embedded microprocessor is provided with an input end, an output end and a control end, the radio frequency switch circuit is realized by adopting a single-pole double-throw switch circuit and is provided with a common end, a first end, a second end and a control end, the output end of the embedded microprocessor is connected with the input end of the radio frequency signal generator, the output end of the radio frequency signal generator is connected with the input end of the radio frequency power amplifying circuit, the output end of the radio frequency power amplifying circuit is connected with the first end of the radio frequency switch circuit, the control end of the radio frequency switch circuit is connected with the control end of the embedded microprocessor, the common end of the radio frequency switch circuit is connected with one end of a radio frequency coil vertical to the direction of the main magnetic field, the other end of the radio frequency coil is grounded, and the second end of the radio frequency switch circuit is connected with the output of the low-noise preamplifier circuit.The input end of the low-noise preamplifier circuit is connected with the input end of the heterodyne locking amplifier circuit, the output end of the heterodyne locking amplifier circuit is connected with the input end of the analog-to-digital conversion circuit, and the output end of the analog-to-digital conversion circuit is connected with the input end of the embedded microprocessor; the embedded microprocessor is internally pre-stored with sweep frequency data, the sweep frequency data comprises a sweep frequency sequence and sweep frequency time, the sweep frequency sequence is formed by arranging a plurality of sweep frequency within a sweep frequency range according to an arithmetic progression form, wherein the first sweep frequency in the sweep frequency sequence is the minimum value of the sweep frequency range, the last sweep frequency in the sweep frequency sequence is the maximum value of the sweep frequency range, and the sweep frequency range is the magnetic field intensity range obtained by measuring and expanding 10% in an actual environment and substituting the Larmor equation w into the magnetic field intensity range B₀Radio frequency range calculated by r, B₀The scanning time is greater than the T2 relaxation time of the detection substance and less than 1.5 times of the T2 relaxation time of the detection substance; when the embedded microprocessor detects each time, the sweep frequency time is taken as a sweep frequency period to periodically sweep frequency and periodically process data, and the sweep frequency period and the data processing period are alternated, wherein the first data processing period is positioned after the first sweep frequency period, the embedded microprocessor outputs the first sweep frequency in the sweep frequency sequence at the output end by default in the first sweep frequency period, in the subsequent sweep frequency period, the embedded microprocessor sequentially outputs other sweep frequency frequencies in the sweep frequency sequence from small to large, the radio frequency signal generator is used for generating radio frequency pulses with the frequency equal to the sweep frequency of the current sweep frequency period in each sweep frequency period and outputting the radio frequency pulses at the output end, the radio frequency power amplifying circuit is used for amplifying the radio frequency pulses output by the radio frequency signal generator to obtain corresponding radio frequency pulses to be output at the output end, the control end of the embedded microprocessor is used for outputting PWM signals, and the PWM signals output by the embedded microprocessor are used for controlling the embedded microprocessorThe common end and the first end of the radio frequency switch circuit are conducted or the common end and the second end of the radio frequency switch circuit are conducted, when the common end and the first end of the radio frequency switch circuit are conducted, the embedded microprocessor controls the analog-digital conversion circuit not to work, when the common end and the second end of the radio frequency switch circuit are conducted, the embedded microprocessor controls the analog-digital conversion circuit to enter a working state for data acquisition and stop working after data acquisition is completed, in each frequency sweeping period, the PWM signal output by the embedded microprocessor controls the common end and the first end of the radio frequency switch circuit to be conducted, at the moment, the radio frequency switch circuit forms a transmitting path, the radio frequency pulse output by the radio frequency power amplifying circuit can be transmitted to the radio frequency coil through the radio frequency switch circuit, and the radio frequency coil generates an electromagnetic field, when a frequency sweep period is finished, the embedded microprocessor enters a data processing period, at the moment, a PWM signal output by the embedded microprocessor controls the conduction of a public end and a second end of a radio frequency switch circuit, the radio frequency switch circuit forms a receiving channel, a radio frequency coil senses a nuclear magnetic resonance echo signal and inputs the nuclear magnetic resonance echo signal into a low-noise preamplifier circuit through the radio frequency switch circuit, the low-noise preamplifier circuit is used for amplifying the received nuclear magnetic resonance echo signal and outputting the nuclear magnetic resonance echo signal, a heterodyne locking amplifier circuit is used for generating an analog envelope signal to output after carrying out frequency spectrum shifting, envelope detection, filtering and low-frequency amplification on the received nuclear magnetic resonance echo signal in sequence, and an analog-to-digital conversion circuit is used for acquiring the analog envelope signal output by the heterodyne locking amplifier circuit and converting the analog envelope signal into a digital envelope signal to output, the input end of the embedded microprocessor is connected with the digital envelope signal output by the analog-to-digital conversion circuit, the digital envelope signal and the frequency sweep frequency of the previous frequency sweep period are bound with each other to be used as a processing data set in the detection process, when the current data processing period is finished, the embedded microprocessor judges whether the frequency sweep frequency of the previous frequency sweep period is the last frequency sweep frequency in the frequency sweep frequency sequence, if not, the embedded microprocessor enters the frequency sweep frequency sequenceDetermining the digital envelope signal with the maximum signal amplitude in all the processing data groups obtained in the detection process if the frequency sweep period is the next frequency sweep period, and finishing the detection by taking the frequency sweep frequency bound by the digital envelope signal as the detected Larmor frequency; before the closed-loop detection system of the low-field nuclear magnetic resonance Larmor frequency carries out detection, firstly, an actual magnetic field intensity range is measured according to gauss in an actual environment, then, the actual magnetic field range is expanded by 10% and is used as a magnetic field intensity range, then, the magnetic field intensity range is substituted into a Larmor equation to obtain a radio frequency range, the radio frequency range is a sweep frequency range, when a detection substance is placed in a nuclear magnetic resonance detection chamber, the closed-loop detection system of the low-field nuclear magnetic resonance Larmor frequency is started, the embedded microprocessor enters detection and starts a sweep frequency period, sweep frequency corresponding to the sweep frequency period is output at an output end of the embedded microprocessor, a PWM signal is output at a control end of the embedded microprocessor to control a first end and a common end of the radio frequency switch circuit to be conducted to form an emission passage, and the radio frequency signal generator generates and outputs corresponding radio frequency pulses, the radio frequency power amplifying circuit amplifies the accessed radio frequency pulse and outputs a corresponding radio frequency pulse, the radio frequency pulse is transmitted to a radio frequency coil vertical to the direction of a main magnetic field through the radio frequency switch circuit, the radio frequency coil generates an electromagnetic field after receiving the radio frequency pulse, protons in a thermal equilibrium state in a detected substance absorb the energy of the radio frequency pulse to generate energy level transition and generate a spin signal, when the frequency sweep period is finished, the control end of the embedded microprocessor enters a data processing period, a PWM signal is output to control the conduction of the second end and the common end of the radio frequency switch circuit, the radio frequency coil does not receive the radio frequency pulse, then the protons in the detected substance are mutually repelled and separated, the synchronous state of the protons is released, and the process is called as T2 or spin relaxation along with the four-dispersed separation of the protons, at the same time the energetic protons will fall back to a low energy state and as these protons return to the baseline, longitudinal magnetization is again formed, which is called "T1" or "spin-lattice relaxation", during which the radio frequency coil will senseThe heterodyne locked amplifying circuit sequentially performs frequency spectrum shifting, envelope detection, filtering and low-frequency amplification on the received nuclear magnetic resonance echo signals to generate analog envelope signals at an mv level and outputs the analog envelope signals at the mv level, the analog-to-digital conversion circuit acquires the analog envelope signals at the mv level in real time, converts the acquired analog envelope signals into digital envelope signals and transmits the digital envelope signals to the embedded microprocessor through a data bus, and the analog-to-digital conversion circuit stops working after data acquisition is finished, at this time, the embedded microprocessor binds the digital Baulo signal acquired by the analog-to-digital conversion circuit this time with the sweep frequency of the previous sweep frequency period and then stores the bound signal as a processing data group, the next sweep frequency period is entered after one data processing period is finished, the sweep frequency of the next sweep frequency period is output by the output end of the embedded microprocessor, and the loop is performed until the processing data group bound with the maximum sweep frequency is obtained, then the embedded microprocessor enters a comprehensive evaluation stage, determines the digital envelope signal with the maximum signal amplitude in all the processing data groups obtained by the detection this time, and uses the sweep frequency bound by the digital envelope signal as the Larmor frequency detected this time, so that the detection is completed.

Compared with the prior art, the invention has the advantages that the closed loop detection system of the low-field nuclear magnetic resonance Larmor frequency is constructed by the embedded microprocessor, the radio frequency signal generator, the radio frequency power amplifying circuit, the radio frequency switch circuit, the low-noise preamplifier circuit, the heterodyne locking amplifying circuit and the analog-to-digital conversion circuit, the embedded microprocessor is provided with an input end, an output end and a control end, the radio frequency switch circuit is realized by adopting a single-pole double-throw switch circuit and is provided with a common end, a first end, a second end and a control end, the output end of the embedded microprocessor is connected with the input end of the radio frequency signal generator, and the radio frequency signal generatorThe output end of the RF power amplifying circuit is connected with the input end of the RF power amplifying circuit, the output end of the RF power amplifying circuit is connected with the first end of the RF switch circuit, the control end of the RF switch circuit is connected with the control end of the embedded microprocessor, the public end of the RF switch circuit is connected with one end of the RF coil vertical to the main magnetic field direction, the other end of the RF coil is grounded, the second end of the RF switch circuit is connected with the input end of the low-noise pre-amplifying circuit, the output end of the low-noise pre-amplifying circuit is connected with the input end of the heterodyne locking amplifying circuit, the output end of the heterodyne locking amplifying circuit is connected with the input end of the analog-to-digital conversion circuit, and the output end of the analog-to-digital conversion circuit is connected with the input end of the embedded microprocessor; the method comprises the steps that sweep frequency data are prestored in the embedded microprocessor, the sweep frequency data comprise a sweep frequency sequence and sweep frequency time, the sweep frequency sequence is formed by arranging a plurality of sweep frequency within a sweep frequency range according to an arithmetic progression form, wherein the first sweep frequency in the sweep frequency sequence is the minimum value of the sweep frequency range, the last sweep frequency in the sweep frequency sequence is the maximum value of the sweep frequency range, and the sweep frequency range is the range of magnetic field intensity measured and expanded by 10% in an actual environment and is substituted into a Larmor equation w to B₀Radio frequency range calculated by r, B₀The magnetic field intensity, w is the radio frequency, r is the magnetic rotation ratio constant, and the sweep time is greater than the T2 relaxation time of the detection substance and less than 1.5 times of the T2 relaxation time of the detection substance; when the embedded microprocessor detects each time, the sweep frequency time is taken as a sweep frequency period to periodically sweep frequency and periodically process data, and the sweep frequency period and the data processing period are alternated, wherein the first data processing period is positioned after the first sweep frequency period, the embedded microprocessor outputs the first sweep frequency in the sweep frequency sequence at the output end by default in the first sweep frequency period, in the subsequent sweep frequency period, the embedded microprocessor outputs other sweep frequency frequencies in the sweep frequency sequence from small to large in sequence, the radio frequency signal generator is used for generating radio frequency pulses with the frequency equal to the sweep frequency of the current sweep frequency period in each sweep frequency period and outputting the radio frequency pulses at the output end, and the radio frequency power amplifying circuit is used for outputting the radio frequency signals at the output end of the radio frequency pulse generatorThe radio frequency pulse output by the generator is amplified to obtain a corresponding radio frequency pulse which is output at the output end of the generator, the control end of the embedded microprocessor is used for outputting a PWM signal, the PWM signal output by the embedded microprocessor is used for controlling the conduction of the public end and the first end of the radio frequency switch circuit or the conduction of the public end and the second end of the radio frequency switch circuit, when the public end and the first end of the radio frequency switch circuit are conducted, the embedded microprocessor controls the analog-digital conversion circuit to enter a working state for data acquisition and stops working after the data acquisition is finished, in each sweep frequency period, the PWM signal output by the embedded microprocessor controls the conduction of the public end and the first end of the radio frequency switch circuit, at the moment, the radio frequency switch circuit forms a transmitting path, and the radio frequency pulse output by the radio frequency power amplifying circuit can be transmitted to the radio frequency coil through the radio frequency switch circuit, the radio frequency coil generates an electromagnetic field, when a sweep frequency period is finished, the embedded microprocessor enters a data processing period, a PWM signal output by the embedded microprocessor controls the conduction of a common end and a second end of the radio frequency switch circuit, the radio frequency switch circuit forms a receiving channel, the radio frequency coil senses a nuclear magnetic resonance echo signal and inputs the nuclear magnetic resonance echo signal into the low-noise preamplification circuit through the radio frequency switch circuit, the low-noise preamplification circuit is used for amplifying the received nuclear magnetic resonance echo signal and outputting the nuclear magnetic resonance echo signal, the heterodyne locking amplifier circuit is used for sequentially carrying out frequency spectrum shifting, envelope detection, filtering and low-frequency amplification on the received nuclear magnetic resonance echo signal to generate an analog envelope signal for output, the analog-to-digital conversion circuit is used for acquiring the analog envelope signal output by the heterodyne locking amplifier circuit and converting the analog envelope signal into a digital envelope signal for output, and the input end of the embedded microprocessor is accessed into the digital envelope signal output by the analog-to-digital conversion circuit, binding the digital envelope signal and the sweep frequency of the previous sweep frequency period with each other to be used as a processing data group in the detection process, judging whether the sweep frequency of the previous sweep frequency period is the last sweep frequency in the sweep frequency sequence by the embedded microprocessor when the current data processing period is finished, if not, entering the next sweep frequency period by the embedded microprocessor,if so, determining the digital envelope signal with the maximum signal amplitude in all the processing data sets obtained in the detection process, and finishing the detection by taking the frequency sweeping frequency bound by the digital envelope signal as the detected Larmor frequency; before the closed-loop detection system of the low-field nuclear magnetic resonance Larmor frequency carries out detection, firstly, the actual magnetic field intensity range is measured according to Gauss in the actual environment, then the actual magnetic field range is expanded by 10% and is used as the magnetic field intensity range, then the magnetic field intensity range is substituted into a Larmor equation to obtain a radio frequency range, the radio frequency range is a sweep frequency range, after a detection substance is placed in a nuclear magnetic resonance detection chamber, the closed-loop detection system of the low-field nuclear magnetic resonance Larmor frequency is started, an embedded microprocessor enters the detection, a sweep frequency period is started, the sweep frequency corresponding to the sweep frequency period is output at the output end of the embedded microprocessor, a PWM signal is output at the control end of the embedded microprocessor to control the first end and the common end of a radio frequency switch circuit to be conducted to form a transmitting channel, a radio frequency signal generator generates and outputs corresponding radio frequency pulses, and a radio frequency power amplification circuit amplifies the accessed radio frequency pulses and outputs corresponding radio frequency pulses, the radio frequency pulse is transmitted to a radio frequency coil vertical to the direction of a main magnetic field through a radio frequency switch circuit, the radio frequency coil generates an electromagnetic field after receiving the radio frequency pulse, protons in a thermal equilibrium state in a detection substance absorb the energy of the radio frequency pulse to generate energy level transition and generate a spin signal, when the frequency sweep period is finished, a control end of an embedded microprocessor enters a data processing period, a PWM signal is output to control the conduction of a second end and a common end of the radio frequency switch circuit, the radio frequency coil does not receive the radio frequency pulse, then protons in the detection substance are mutually exclusive and separated, the synchronous state of the protons is released, along with the scattered separation of the protons, the process is called T2 or spin relaxation, high-energy protons fall back to a low-energy state, along with the protons return to a base line, longitudinal magnetization is formed again, the process is called as T1 or spin relaxation lattice, in the proton regression process of 'spin relaxation' and 'spin-lattice relaxation', a radio frequency coil induces a weak echo signal generated by a magnetic induction line of a cutting main magnetic field when the proton is regressed, namely a nuclear magnetic resonance echo signalA low-noise preamplification circuit is transmitted through a radio frequency switch circuit, the low-noise preamplification circuit amplifies nuclear magnetic resonance echo signals to obtain nuclear magnetic resonance echo signal output with high signal-to-noise ratio after amplification, a heterodyne locking amplification circuit sequentially carries out frequency spectrum shifting, envelope detection, filtering and low-frequency amplification on the received nuclear magnetic resonance echo signals to generate analog envelope signals at mv level for output, an analog-to-digital conversion circuit acquires the analog envelope signals at mv level in real time, converts the acquired analog envelope signals into digital envelope signals and transmits the digital envelope signals to an embedded microprocessor through a data bus, the analog-to-digital conversion circuit stops working after data acquisition, and the embedded microprocessor binds the digital envelope signals acquired by the analog-to-digital conversion circuit with the frequency sweep frequency of the previous frequency sweep period and then stores the digital envelope signals as a processing data group, entering the next sweep frequency period after a data processing period is finished, outputting the sweep frequency of the next sweep frequency period by the output end of the embedded microprocessor, circulating the sweep frequency until a processing data group bound with the maximum sweep frequency is obtained, then entering a comprehensive evaluation stage by the embedded microprocessor, determining a digital envelope signal with the maximum signal amplitude in all the processing data groups obtained by the detection, taking the sweep frequency bound with the digital envelope signal as the Larmor frequency detected at this time, and completing the detection. And finally, the frequency of the sweep frequency bound by the digital envelope signal with the maximum signal amplitude is used as the detected Larmor frequency, so that the detection result is not influenced by factors such as the detection environment, the magnet processing precision, the magnet structure design error and the like, and the Larmor frequency detection precision is higher.

Drawings

Fig. 1 is a schematic structural diagram of a closed-loop detection system of low-field nuclear magnetic resonance Larmor frequency according to the present invention.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

Example (b): as shown in fig. 1, a closed loop detection system of low-field nuclear magnetic resonance Larmor frequency includes an embedded microprocessor, a radio frequency signal generator, a radio frequency power amplifying circuit, a radio frequency switch circuit, a low-noise pre-amplifying circuit, a heterodyne locking amplifying circuit and an analog-to-digital conversion circuit; the embedded microprocessor is provided with an input end, an output end and a control end, the radio frequency switch circuit is realized by adopting a single-pole double-throw switch circuit and is provided with a common end, a first end, a second end and a control end, the output end of the embedded microprocessor is connected with the input end of the radio frequency signal generator, the output end of the radio frequency signal generator is connected with the input end of the radio frequency power amplifying circuit, the output end of the radio frequency power amplifying circuit is connected with the first end of the radio frequency switch circuit, the control end of the radio frequency switch circuit is connected with the control end of the embedded microprocessor, the common end of the radio frequency switch circuit is connected with one end of a radio frequency coil vertical to the direction of a main magnetic field, the other end of the radio frequency coil is grounded, the second end of the radio frequency switch circuit is connected with the input end of a low-noise preamplifier circuit, the output end of the low-noise preamplifier circuit is connected with the input end of a heterodyne locking amplifier circuit, the output end of the heterodyne locking amplifying circuit is connected with the input end of the analog-to-digital conversion circuit, and the output end of the analog-to-digital conversion circuit is connected with the input end of the embedded microprocessor; the method comprises the steps that sweep frequency data are prestored in the embedded microprocessor, the sweep frequency data comprise a sweep frequency sequence and sweep frequency time, the sweep frequency sequence is formed by arranging a plurality of sweep frequency within a sweep frequency range according to an arithmetic progression form, wherein the first sweep frequency in the sweep frequency sequence is the minimum value of the sweep frequency range, the last sweep frequency in the sweep frequency sequence is the maximum value of the sweep frequency range, and the sweep frequency range is the range of magnetic field intensity measured and expanded by 10% in an actual environment and is substituted into a Larmor equation w to B₀Radio frequency range calculated by r, B₀The magnetic field intensity, w is the radio frequency, r is the magnetic rotation ratio constant, and the sweep time is larger than the T2 relaxation time of the detected substance and smaller than 1.5 timesMeasuring the T2 relaxation time of the substance; when the embedded microprocessor detects each time, the sweep frequency time is taken as a sweep frequency period to periodically sweep frequency and periodically process data, and the sweep frequency period and the data processing period are alternated, wherein the first data processing period is positioned after the first sweep frequency period, in the first sweep frequency period, the embedded microprocessor outputs the first sweep frequency in the sweep frequency sequence by default at the output end, in the subsequent sweep frequency period, the embedded microprocessor outputs other sweep frequency frequencies in the sweep frequency sequence from small to large in sequence, the radio frequency signal generator is used for generating radio frequency pulses with the frequency equal to the sweep frequency of the current sweep frequency period in each sweep frequency period and outputting the radio frequency pulses at the output end, the radio frequency power amplifying circuit is used for amplifying the radio frequency pulses output by the radio frequency signal generator to obtain corresponding radio frequency pulses and outputting the corresponding radio frequency pulses at the output end, the control end of the embedded microprocessor is used for outputting PWM signals, the PWM signals output by the embedded microprocessor are used for controlling the conduction of the public end and the first end or the conduction of the public end and the second end of the radio frequency switch circuit, when the public end and the first end of the radio frequency switch circuit are conducted, the embedded microprocessor controls the analog-digital conversion circuit not to work, when the public end and the second end of the radio frequency switch circuit are conducted, the embedded microprocessor controls the analog-digital conversion circuit to enter a working state for data acquisition and stop working after the data acquisition is finished, in each frequency sweeping period, the PWM signals output by the embedded microprocessor control the conduction of the public end and the first end of the radio frequency switch circuit, at the moment, the radio frequency switch circuit forms a transmitting path, radio frequency pulses output by the radio frequency power amplifying circuit can be transmitted to the radio frequency coil through the radio frequency switch circuit, and the radio frequency coil generates an electromagnetic field, when a sweep frequency period is finished, the embedded microprocessor enters a data processing period, the PWM signal output by the embedded microprocessor controls the conduction of the public end and the second end of the radio frequency switch circuit, the radio frequency switch circuit forms a receiving channel, the radio frequency coil senses the nuclear magnetic resonance echo signal and inputs the nuclear magnetic resonance echo signal into the low-noise pre-amplification circuit through the radio frequency switch circuit, the low-noise pre-amplification circuit is used for amplifying and outputting the received nuclear magnetic resonance echo signal, and the heterodyne locking amplification circuit is used for locking and amplifying the nuclear magnetic resonance echo signalThe method comprises the steps of carrying out frequency spectrum shifting, envelope detection, filtering and low-frequency amplification on a received nuclear magnetic resonance echo signal in sequence to generate an analog envelope signal for output, using an analog-to-digital conversion circuit to acquire an analog envelope signal output by a heterodyne lock amplification circuit and convert the analog envelope signal into a digital envelope signal for output, using an input end of an embedded microprocessor to access the digital envelope signal output by the analog-to-digital conversion circuit, binding the digital envelope signal and the frequency sweep frequency of a previous frequency sweep period to be a processing data set in the detection process, judging whether the frequency sweep frequency of the previous frequency sweep period is the last frequency sweep frequency in a frequency sweep frequency sequence or not by the embedded microprocessor when the current data processing period is ended, entering the next frequency sweep period if not, and determining the digital envelope signal with the maximum signal amplitude in all the processing data sets obtained in the detection process if the current data processing period is ended, the frequency of the sweep frequency bound by the digital envelope signal is used as the detected Larmor frequency, and the detection is finished; before the closed-loop detection system of the low-field nuclear magnetic resonance Larmor frequency carries out detection, firstly, the actual magnetic field intensity range is measured according to Gauss in the actual environment, then the actual magnetic field range is expanded by 10% and is used as the magnetic field intensity range, then the magnetic field intensity range is substituted into a Larmor equation to obtain a radio frequency range, the radio frequency range is a sweep frequency range, after a detection substance is placed in a nuclear magnetic resonance detection chamber, the closed-loop detection system of the low-field nuclear magnetic resonance Larmor frequency is started, an embedded microprocessor enters the detection, a sweep frequency period is started, the sweep frequency corresponding to the sweep frequency period is output at the output end of the embedded microprocessor, a PWM signal is output at the control end of the embedded microprocessor to control the first end and the common end of a radio frequency switch circuit to be conducted to form a transmitting channel, a radio frequency signal generator generates and outputs corresponding radio frequency pulses, and a radio frequency power amplification circuit amplifies the accessed radio frequency pulses and outputs corresponding radio frequency pulses, the radio frequency pulse is transmitted to a radio frequency coil vertical to the direction of the main magnetic field through a radio frequency switch circuit, the radio frequency coil generates an electromagnetic field after receiving the radio frequency pulse, at the moment, protons in a thermal equilibrium state in a detection substance absorb the energy of the radio frequency pulse to generate energy level transition and generate a spinning signal, and when the frequency sweeping period is finished at this timeWhen the beam is formed, the control end of the embedded microprocessor enters a data processing period, a PWM signal is output to control the second end of the radio frequency switch circuit and the common end to be conducted, at the moment, the radio frequency coil does not receive radio frequency pulses any more, then, protons in the detected substance are mutually repelled and separated, the synchronous state of the protons is released, along with the scattered separation of the protons, the process is called T2 or spin relaxation, simultaneously, high-energy protons fall back to a low-energy state, along with the return of the protons to a base line, longitudinal magnetization is formed again, which is called T1 or spin-lattice relaxation, during the proton regression process of the spin relaxation and the spin-lattice relaxation, the radio frequency coil induces a weak echo signal generated by cutting a main magnetic field induction line when the protons return, namely a nuclear magnetic resonance echo signal, and transmits a low-noise preamplifier circuit through the radio frequency switch circuit, the low-noise preamplification circuit amplifies nuclear magnetic resonance echo signals to obtain nuclear magnetic resonance echo signal output with high signal-to-noise ratio after amplification, the heterodyne locking amplification circuit sequentially carries out frequency spectrum shifting, envelope detection, filtering and low-frequency amplification on the received nuclear magnetic resonance echo signals to generate analog envelope signal output at an mv level, the analog-to-digital conversion circuit collects analog envelope signals at the mv level in real time, converts the collected analog envelope signals into digital envelope signals and transmits the digital envelope signals to the embedded microprocessor through a data bus, the embedded microprocessor stops working after data collection is finished, the digital envelope signals collected by the analog-to-digital conversion circuit are bound with the frequency sweep frequency of the previous frequency sweep period and then are stored as a processing data group, and the next frequency sweep period is started after one data processing period is finished, and the output end of the embedded microprocessor outputs the frequency sweep frequency of the next frequency sweep period, and the cycle is carried out until a processing data group bound with the maximum frequency sweep frequency is obtained, then the embedded microprocessor enters a comprehensive evaluation stage, determines a digital envelope signal with the maximum signal amplitude in all the processing data groups obtained by the detection, and finishes the detection by taking the frequency sweep frequency bound with the digital envelope signal as the detected Larmor frequency.

Claims (1)

Translated fromChinese

1.一种低场核磁共振Larmor频率的闭环检测系统，其特征在于包括嵌入式微处理器、射频信号发生器、射频功率放大电路、射频开关电路、低噪前置放大电路，外差式锁定放大电路和模数转换电路；所述的嵌入式微处理器具有输入端、输出端和控制端，所述的射频开关电路采用单刀双掷开关电路实现，具有公共端、第一端、第二端和控制端，所述的嵌入式微处理器的输出端和所述的射频信号发生器的输入端连接，所述的射频信号发生器的输出端和所述的射频功率放大电路的输入端连接，所述的射频功率放大电路的输出端和所述的射频开关电路的第一端连接，所述的射频开关电路的控制端和所述的嵌入式微处理器的控制端连接，所述的射频开关电路的公共端和垂直于主磁场方向的射频线圈的一端连接，射频线圈的另一端接地，所述的射频开关电路的第二端和所述的低噪前置放大电路的输入端连接，所述的低噪前置放大电路的输出端和所述的外差式锁定放大电路的输入端连接，所述的外差式锁定放大电路的输出端和所述的模数转换电路的输入端连接，所述的模数转换电路的输出端和所述的嵌入式微处理器的输入端连接；1. A closed-loop detection system of low-field nuclear magnetic resonance Larmor frequency is characterized in that comprising embedded microprocessor, radio frequency signal generator, radio frequency power amplifier circuit, radio frequency switch circuit, low noise preamplifier circuit, heterodyne lock-in amplifier circuit and analog-to-digital conversion circuit; the embedded microprocessor has an input end, an output end and a control end, the radio frequency switch circuit is realized by a single-pole double-throw switch circuit, and has a common end, a first end, a second end and a control end. The control end, the output end of the embedded microprocessor is connected with the input end of the radio frequency signal generator, the output end of the radio frequency signal generator is connected with the input end of the radio frequency power amplifier circuit, so The output end of the radio frequency power amplifier circuit is connected to the first end of the radio frequency switch circuit, the control end of the radio frequency switch circuit is connected to the control end of the embedded microprocessor, and the radio frequency switch circuit The common end is connected to one end of the radio frequency coil perpendicular to the direction of the main magnetic field, the other end of the radio frequency coil is grounded, the second end of the radio frequency switch circuit is connected to the input end of the low-noise preamplifier circuit, the The output end of the low-noise preamplifier circuit is connected with the input end of the heterodyne lock-in amplifier circuit, the output end of the heterodyne lock-in amplifier circuit is connected with the input end of the analog-to-digital conversion circuit, The output end of the analog-to-digital conversion circuit is connected with the input end of the embedded microprocessor;所述的嵌入式微处理器内部预存有扫频数据，所述的扫频数据包含扫频频率序列和扫频时间，所述的扫频频率序列由扫频频率范围内多个扫频频率按照等差数列形式排列形成，其中，所述的扫频频率序列中第一个扫频频率为扫频频率范围的最小值，所述的扫频频率序列中最后一个扫频频率为扫频频率范围的最大值，所述的扫频频率范围即为通过在实际环境中测得并扩大10％后的磁场强度范围代入拉莫尔方程w＝B₀*r计算所得的射频频率范围，B₀为磁场强度，w为射频频率，r为磁旋比常数，所述的扫频时间大于检测物质的T2驰豫时间且小于1.5倍的检测物质的T2驰豫时间；The embedded microprocessor is internally pre-stored with sweep frequency data, the sweep frequency data includes sweep frequency sequence and sweep time, and the sweep frequency sequence is composed of multiple sweep frequencies within the sweep frequency range according to equal The difference sequence is arranged in the form, wherein, the first sweep frequency in the sweep frequency sequence is the minimum value of the sweep frequency range, and the last sweep frequency in the sweep frequency sequence is the minimum value of the sweep frequency range. The maximum value, the sweep frequency range is the RF frequency range calculated by substituting the magnetic field strength range measured in the actual environment and expanded by 10% into the Larmor equation w=B₀ *r, where B₀ is the magnetic field Intensity, w is the radio frequency, r is the magnetic spin ratio constant, the frequency sweep time is greater than the T2 relaxation time of the detection material and less than 1.5 times the T2 relaxation time of the detection material;所述的嵌入式微处理器每次进行检测时，以扫频时间作为一个扫频周期来周期性的进行扫频以及周期性的进行数据处理，且扫频周期和数据处理周期交替，其中第一个数据处理周期位于第一个扫频周期之后，在第一个扫频周期，所述的嵌入式微处理器在其输出端默认输出扫频频率序列中第一个扫频频率，在后续扫频周期中，所述的嵌入式微处理器将扫频频率序列中其他扫频频率从小到大依次输出，所述的射频信号发生器用于在每个扫频周期产生频率等于当前扫频周期的扫频频率的射频脉冲在其输出端输出，所述的射频功率放大电路用于对所述的射频信号发生器输出的射频脉冲进行放大得到相应的射频脉冲在其输出端输出，所述的嵌入式微处理器的控制端用于输出PWM信号，所述的嵌入式微处理器输出的PWM信号用于控制所述的射频开关电路的公共端和第一端导通或者公共端和第二端导通，在所述的射频开关电路的公共端和第一端导通时，所述的嵌入式微处理器控制所述的模数转换电路不工作，在所述的射频开关电路的公共端和第二端导通时，所述的嵌入式微处理器控制所述的模数转换电路进入工作状态进行数据采集，并在完成数据采集后停止工作，在每个扫频周期，所述的嵌入式微处理器输出的PWM信号控制所述的射频开关电路的公共端和第一端导通，此时所述的射频开关电路形成发射通路，所述的射频功率放大电路输出的射频脉冲能够通过所述的射频开关电路输送至射频线圈，射频线圈产生电磁场，当在一个扫频周期结束时，所述的嵌入式微处理器进入一个数据处理处理周期，此时所述的嵌入式微处理器输出的PWM信号控制所述的射频开关电路的公共端和第二端导通，所述的射频开关电路形成接收通路，射频线圈感应到核磁共振回波信号并通过所述的射频开关电路输入所述的低噪前置放大电路，所述的低噪前置放大电路用于放大接收到的核磁共振回波信号并输出，所述的外差式锁定放大电路用于对接收到的核磁共振回波信号依次进行频谱搬移、包络检波、滤波以及低频放大后生成模拟包络信号输出，所述的模数转换电路用于采集所述的外差式锁定放大电路输出的模拟包络信号并将其转换为数字包络信号输出，所述的嵌入式微处理器的输入端接入所述的模数转换电路输出的数字包络信号，并将该数字包络信号与前一个扫频周期的扫频频率相互绑定作为本次检测过程中的一个处理数据组，当当前数据处理周期结束时，所述的嵌入式微处理器判断前一个扫频周期的扫频频率是否为扫频频率序列中最后一个扫频频率，如果不是，所述的嵌入式微处理器进入下一个扫频周期，如果是，则确定本次检测过程中得到的所有处理数据组中信号幅度最大的数字包络信号，将该数字包络信号绑定的扫频频率作为检测到的Larmor频率，检测完成；Each time the embedded microprocessor performs detection, the frequency sweep time is used as a frequency sweep cycle to periodically sweep the frequency and periodically perform data processing, and the frequency sweep cycle and the data processing cycle alternate. The first data processing cycle is located after the first frequency sweep cycle. In the first frequency sweep cycle, the embedded microprocessor outputs the first sweep frequency in the sweep frequency sequence by default at its output, and in the subsequent sweep frequency During the cycle, the embedded microprocessor sequentially outputs other sweep frequencies in the sweep frequency sequence from small to large, and the radio frequency signal generator is used to generate sweep frequencies with a frequency equal to the current sweep cycle in each sweep cycle. The radio frequency pulse of the frequency is output at its output end, and the radio frequency power amplifier circuit is used to amplify the radio frequency pulse output by the radio frequency signal generator to obtain the corresponding radio frequency pulse output at its output end, and the embedded microprocessor The control terminal of the device is used to output PWM signal, and the PWM signal output by the embedded microprocessor is used to control the conduction between the common terminal and the first terminal of the radio frequency switch circuit or the conduction between the common terminal and the second terminal. When the common terminal and the first terminal of the radio frequency switch circuit are turned on, the embedded microprocessor controls the analog-to-digital conversion circuit to not work, and the common terminal and the second terminal of the radio frequency switch circuit conduct electricity. When it is on, the embedded microprocessor controls the analog-to-digital conversion circuit to enter the working state for data acquisition, and stops working after completing the data acquisition. In each frequency sweep cycle, the embedded microprocessor outputs The PWM signal controls the common terminal and the first terminal of the radio frequency switch circuit to conduct. At this time, the radio frequency switch circuit forms a transmission path, and the radio frequency pulse output by the radio frequency power amplifier circuit can pass through the radio frequency switch circuit. It is sent to the radio frequency coil, and the radio frequency coil generates an electromagnetic field. When a frequency sweep cycle ends, the embedded microprocessor enters a data processing cycle, and the PWM signal output by the embedded microprocessor controls the The common terminal and the second terminal of the radio frequency switch circuit are connected, the radio frequency switch circuit forms a receiving path, and the radio frequency coil senses the NMR echo signal and inputs it to the low-noise preamplifier circuit through the radio frequency switch circuit , the low-noise preamplifier circuit is used to amplify the received NMR echo signals and output them, and the heterodyne lock-in amplifier circuit is used to sequentially perform spectrum shifting, packetization, etc. on the received NMR echo signals The analog envelope signal output is generated after envelope detection, filtering and low-frequency amplification, and the analog-to-digital conversion circuit is used to collect the analog envelope signal output by the heterodyne lock-in amplifier circuit and convert it into a digital envelope signal output. , the input end of the embedded microprocessor is connected to the digital envelope signal output by the analog-to-digital conversion circuit, and the digital envelope signal and the sweep frequency of the previous sweep cycle are bound to each other as the current frequency. A processing data group in the detection process, when the current data processing cycle ends, the embedded microprocessor determines whether the sweep frequency of the previous sweep cycle is the last sweep frequency in the sweep frequency sequence, if not , the embedded microprocessor enters the next frequency sweep cycle, if so, determine the digital envelope signal with the largest signal amplitude in all the processed data groups obtained in this detection process, and bind the digital envelope signal to the The sweep frequency is used as the detected Larmor frequency, and the detection is completed;当所述的低场核磁共振Larmor频率的闭环检测系统进行检测之前，先在实际环境中根据高斯计测得实际磁场强度范围，然后将实际磁场范围扩大10％后最为磁场强度范围，接着将该磁场强度范围代入拉莫尔方程得到射频频率范围，该射频频率范围即为扫频频率范围，当检测物质被放置于核磁共振检测室后，所述的低场核磁共振Larmor频率的闭环检测系统启动，所述的嵌入式微处理器进入检测，开始一个扫频周期，在其输出端输出该扫频周期对应的扫频频率，并在其控制端输出PWM信号控制所述的射频开关电路的第一端和公共端导通形成发射通路，所述的射频信号发生器产生并输出相应的射频脉冲，所述的射频功率放大电路对接入的射频脉冲进行放大并输出相应的射频脉冲，该射频脉冲通过所述的射频开关电路输送至垂直于主磁场方向的射频线圈，射频线圈接收到射频脉冲后产生电磁场，此时检测物质中处于热平衡状态的质子将吸收射频脉冲能量发生能级跃迁并产生自旋信号，当本次扫频周期结束时，所述的嵌入式微处理器的控制端进入一个数据处理周期，输出PWM信号控制所述的射频开关电路的第二端和公共端导通，此时射频线圈不再接收射频脉冲，随后检测物质中的质子会相互排斥并分离，质子的同步状态解除，随着他们四散分离，这个过程叫“T2”或“自旋驰豫”，同时高能质子将回落到低能状态，随着这些质子回到基线，再次形成了纵向磁化，这被称之为“T1”或“自旋-点阵驰豫”，在“自旋驰豫”和“自旋-点阵驰豫”的质子回归过程中，射频线圈将感应到质子回归时切割主磁场磁感线所产生的微弱回波信号，即核磁共振回波信号，并通过所述的射频开关电路传递所述的低噪前置放大电路，所述的低噪前置放大电路对核磁共振回波信号进行放大获得放大后的信噪比高的核磁共振回波信号输出，所述的外差式锁定放大电路对接收到的核磁共振回波信号依次进行频谱搬移、包络检波、滤波以及低频放大后产生mv级别的模拟包络信号输出，所述的模数转换电路实时采集mv级别的模拟包络信号，并将采集到的模拟包络信号转化为数字包络信号并通过数据总线传送给所述的嵌入式微处理器，所述的模数转换电路数据采集结束后停止工作，此时所述的嵌入式微处理器将所述的模数转换电路本次采集到的数字包洛信号与前一个扫频周期的扫频频率进行绑定后作为一个处理数据组保存，一个数据处理周期结束后进入下一个扫频周期，所述的嵌入式微处理器的输出端输出下一个扫频周期的扫频频率，以此循环，直至得到与最大扫频频率绑定形成的处理数据组，然后所述的嵌入式微处理器将进入综合评估阶段，确定本次检测得到的所有处理数据组中信号幅度最大的数字包络信号，将该数字包络信号绑定的扫频频率作为本次检测到的Larmor频率，检测完成。Before the low-field nuclear magnetic resonance Larmor frequency closed-loop detection system performs detection, the actual magnetic field strength range is measured according to the Gauss meter in the actual environment, and then the actual magnetic field strength range is expanded by 10% to the maximum magnetic field strength range. Substitute the magnetic field strength range into the Larmor equation to obtain the radio frequency range, which is the sweep frequency range. When the test substance is placed in the NMR test room, the low-field nuclear magnetic resonance Larmor frequency closed-loop detection system is activated. , the embedded microprocessor enters the detection, starts a frequency sweep cycle, outputs the sweep frequency corresponding to the frequency sweep cycle at its output end, and outputs a PWM signal at its control end to control the first frequency of the radio frequency switch circuit. The radio frequency signal generator generates and outputs corresponding radio frequency pulses, and the radio frequency power amplifier circuit amplifies the connected radio frequency pulses and outputs corresponding radio frequency pulses. The radio frequency switch circuit is sent to the radio frequency coil perpendicular to the direction of the main magnetic field, and the radio frequency coil generates an electromagnetic field after receiving the radio frequency pulse. At this time, the protons in the thermal equilibrium state in the detection material will absorb the energy of the radio frequency pulse to generate energy level transition and generate self- When the frequency sweep cycle ends, the control end of the embedded microprocessor enters a data processing cycle, and outputs a PWM signal to control the second end and the common end of the radio frequency switch circuit to conduct, at this time The radio frequency coil no longer receives the radio frequency pulse, and then the protons in the detection material will repel and separate from each other, the synchronization state of the protons is released, and as they disperse, this process is called "T2" or "spin relaxation", and the high-energy protons will Falling back to a lower energy state, as these protons return to the baseline, longitudinal magnetization is formed again, which is called "T1" or "spin-lattice relaxation", between "spin relaxation" and "spin-lattice relaxation" In the proton regression process of "lattice relaxation", the radio frequency coil will sense the weak echo signal generated by cutting the magnetic field line of the main magnetic field when the proton returns, that is, the nuclear magnetic resonance echo signal, and transmit all the signals through the radio frequency switch circuit. The low-noise pre-amplifier circuit, the low-noise pre-amplifier circuit amplifies the nuclear magnetic resonance echo signal to obtain the amplified nuclear magnetic resonance echo signal output with high signal-to-noise ratio, the heterodyne lock-in amplification The circuit sequentially performs spectrum shifting, envelope detection, filtering and low-frequency amplification on the received NMR echo signal to generate an analog envelope signal output at the mv level. The analog-to-digital conversion circuit collects the analog envelope signal at the mv level in real time. , and convert the collected analog envelope signal into a digital envelope signal and transmit it to the embedded microprocessor through the data bus, the analog-to-digital conversion circuit stops working after data collection, and the embedded The microprocessor binds the digital packet signal collected by the analog-to-digital conversion circuit this time with the sweep frequency of the previous sweep cycle and saves it as a processing data group. After one data processing cycle ends, it enters the next frequency sweep cycle, the output terminal of the embedded microprocessor outputs the sweep frequency of the next frequency sweep cycle, and this cycle , until the processing data group bound with the maximum frequency sweep frequency is obtained, and then the embedded microprocessor will enter the comprehensive evaluation stage to determine the digital envelope signal with the largest signal amplitude in all the processing data groups obtained by this detection, The sweep frequency bound to the digital envelope signal is taken as the Larmor frequency detected this time, and the detection is completed.

Images