Plug-in type multi-nuclide multichannel synchronous MRI real-time electromagnetic energy absorption rate monitoring system

Abstract

The invention discloses a plug-in type multi-nuclide multichannel synchronous MRI (Magnetic Resonance Imaging) real-time electromagnetic energy absorptivity monitoring system, which relates to the technical field of MRI imaging and comprises a plurality of plug-in type radio frequency power measuring units and a group of multi-nuclide electromagnetic energy absorptivity control digital signal processing units, the plug-in type radio frequency power measuring unit is inserted into a radio frequency link of the multi-nuclide parallel MRI system in a plug-in mode, and the multi-nuclide electromagnetic energy absorption rate control digital signal processing unit is used for receiving a radio frequency power signal and calculating the electromagnetic energy absorption rate and interacts with a multi-nuclide synchronous imaging control spectrometer to control the scanning process. The multi-nuclide multi-channel electromagnetic energy absorption rate is calculated by using a transmission line matrix method, the radio frequency power measurement unit is inserted into a multi-nuclide parallel MRI system or a conventional MRI system in a plug-in mode, an original radio frequency link of the system does not need to be changed, original imaging conditions are not influenced, and the method has good practical performance.

Description

Technical Field

[0001] This invention relates to the field of MRI imaging technology, specifically a plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system. Background Technology

[0002] MRI imaging is a medical imaging modality that allows observation of the internal structure and function of the human body without the use of X-rays or other ionizing radiation. Most existing MRI systems utilize... 1 Single-nuclide imaging systems using H protons as imaging nuclides contain only a single type of information. However, organisms are complex multi-nuclide and multi-molecular systems. In order to obtain information about the structure, function, and spatiotemporally related events at the molecular level from different nuclides in a non-invasive manner, multi-nuclide MRI has become a hot topic in the industry.

[0003] Multi-nuclide MRI systems typically contain multiple radio frequency channels with different resonant frequencies. Each nuclide corresponds to an independent radio frequency link, involving multi-band radio frequency power amplifiers, multi-nuclide parallel coil units, etc. The radio frequency, power, and field distribution characteristics of each nuclide vary, resulting in complex electromagnetic energy absorption in human tissues. Although relevant international and domestic safety standards (such as FDA, IEC, and YY) have stipulated safe thresholds for electromagnetic energy absorption rates in the human body during MRI to avoid radio frequency energy burns / damage to subjects, current monitoring technologies are only applicable to single-nuclide systems. There is still a lack of corresponding methods or systems for monitoring electromagnetic energy absorption rates in multi-nuclide MRI systems. In multi-nuclide simultaneous imaging scenarios, it is impossible to monitor the electromagnetic energy absorption rate of each nuclide in real time, both locally and globally. Consequently, it is impossible to safely control the scanning process, leading to a failure to guarantee subject safety and thus limiting the development of multi-nuclide MRI technology.

[0004] Based on this, a plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system is now provided, which can eliminate the drawbacks of existing technical solutions. Summary of the Invention

[0005] The purpose of this invention is to provide a plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system to solve the problem in the prior art that existing multi-nucleoside synchronous imaging scenarios cannot perform real-time local and global monitoring of multi-nucleoside electromagnetic energy absorption rate.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A plug-in multi-nuclide multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system includes several plug-in radio frequency power measurement units and a set of multi-nuclide electromagnetic energy absorption rate control digital signal processing units. The plug-in radio frequency power measurement units are inserted into the radio frequency link of the multi-nuclide parallel MRI system in the form of plug-ins. The multi-nuclide electromagnetic energy absorption rate control digital signal processing units are used to receive radio frequency power signals and calculate electromagnetic energy absorption rate, and interact with the multi-nuclide synchronous imaging control spectrometer to control the scanning process. The plug-in RF power measurement unit includes a bidirectional directional coupler, a true RMS response detector, a fully differential amplifier, an analog-to-digital converter (ADC), and an electro-optical converter. The bidirectional directional coupler couples forward and reflected power from different RF channels to the outside of the RF link. The ADC enables high-precision RF power detection and outputs the power signal as a voltage signal. The fully differential amplifier calculates the difference between incident and reflected power and obtains the coil RF energy absorption rate for each nuclide and each channel. The ADC converts analog signals to digital signals, and the electro-optical converter converts digital electrical signals to optical signals, which are then transmitted to the multi-nuclide RF energy absorption rate control digital signal processing unit for processing. The plug-in radio frequency power measurement unit is installed on the side of the magnet near the coil. The multi-nuclide radio frequency energy absorption rate control digital signal processing unit is installed on the side of the multi-nuclide multi-channel MRI imaging device near the multi-nuclide synchronous imaging control spectrometer. The electro-optical conversion module of the plug-in radio frequency power measurement unit and the photoelectric conversion module of the multi-nuclide radio frequency energy absorption rate control digital signal processing unit transmit optical signals through optical fiber and waveguides on the filter board to avoid introducing interference.

[0007] Furthermore, the multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit includes a photoelectric conversion module, a microprocessor, and a memory. The photoelectric conversion module is used to convert the optical signal calculated by the plug-in radio frequency power measurement unit into a digital electrical signal. The microprocessor is used to calculate the electromagnetic energy absorption rate estimate based on the real-time sampled digital electrical signal, compare it with the safety threshold accessed in real time by the memory, and send a corresponding scan signal based on the comparison result.

[0008] Furthermore, the multi-nucleus parallel MRI system achieves radio frequency timing control through a multi-nucleus synchronous imaging control spectrometer, and has multiple radio frequency links with the same structure but designed for different nuclides. The radio frequency excitation component of each nuclide's radio frequency link includes a radio frequency power amplifier, power divider, synchronous transmit / receive switch, synchronous resonance / detuning switch, plug-in radio frequency power measurement unit, and multi-nucleus parallel synchronous multi-channel coil unit for the corresponding nuclide. The multi-nucleus synchronous imaging control spectrometer sends low-power radio frequency pulses of various frequencies and waveforms to the radio frequency power amplifier of the corresponding nuclide. The high-power radio frequency signal amplified by the radio frequency power amplifier enters the radio frequency shielding chamber through a filter board. Each nuclide's high-power signal is divided into multiple channels with equal phase by a power divider. The high-power radio frequency pulse of each channel is fed into the multi-nucleus parallel synchronous multi-channel coil unit after passing through the synchronous transmit / receive switch and the synchronous resonance / detuning switch.

[0009] Furthermore, the microprocessor employs the transmission line matrix method to perform real-time numerical simulation of the electric field energy distribution at each spatial node of the multi-nucleoside multi-channel radio frequency excitation source at each moment, thereby calculating the local electromagnetic energy absorption rate.

[0010] Furthermore, the process by which the microprocessor calculates the local electromagnetic energy absorption rate includes: The entire three-dimensional space for calculating the field distribution is discretized into a grid composed of TLM nodes. Electromagnetic properties are assigned to the nodes and a perfectly matched layer absorption boundary condition is set at the grid boundary. The source point and excitation signal corresponding to each radio frequency channel of each nuclide are defined, and the scattering matrix of the imaging region is established. After completing the initial condition setting, the time step iteration loop is entered. The time step is set according to the total duration of multi-nucleus synchronous imaging. The excitation pulses of each nuclide and each channel are injected into the node. At each node, all incident pulses will arrive at the node center at the same time, simulating the reflection and interaction of electromagnetic waves on the medium node. The scattered pulses of the incident pulses at the adjacent nodes are simulated and calculated according to the scattering matrix of the imaging area. The pulses scattered by each node will become the incident pulses of the neighboring nodes in the next time step. The pulse voltage and current at the grid location are read, and the corresponding electric field intensity is calculated according to the electric field intensity formula. When the time step does not reach the maximum value, the local electromagnetic energy absorption rate at each moment is calculated according to the electromagnetic energy absorption rate formula. After averaging in the time domain, the average electromagnetic energy at each grid location in the short and long time periods is calculated respectively. The maximum value at all grid locations in the short time period is taken as the final result of the local short-time electromagnetic energy absorption rate, and the maximum value at all grid locations in the long time period is taken as the final result of the local long-time electromagnetic energy absorption rate.

[0011] Furthermore, the security thresholds include a global long-time threshold, a global short-time threshold, a radio frequency power correction factor for each channel of each nuclide, a magnetoresistive ratio for each nuclide, and local long-time thresholds and local short-time thresholds stored according to different locations.

[0012] Furthermore, the process by which the microprocessor calculates the estimated electromagnetic energy absorption rate includes: The microprocessor samples the radio frequency power (RF) values ​​from the plug-in RF power measurement units of each nuclide and each channel. It then corrects these RF power values ​​using a corresponding RF power correction factor. The gyromagnetic ratio for each nuclide is used as the nuclide coefficient. The real-time electromagnetic energy absorption rate is calculated using the RF power correction factor. The real-time RF energy absorption rate of each nuclide and each channel is shifted and buffered. The buffer matrix is ​​sampled at the beginning, and the real-time RF energy absorption rate is collected for both short and long-term periods. These are averaged over time to obtain the short-term and long-term RF energy absorption rates, respectively. The short-term and long-term RF energy absorption rates of each nuclide and each channel are then weighted and summed to obtain the real-time estimation results of the global short-term and global long-term RF energy absorption rates for each nuclide and each channel.

[0013] Furthermore, the process by which the microprocessor sends a corresponding scan signal based on the comparison result includes: The global short-time electromagnetic energy absorption rate, global long-time electromagnetic energy absorption rate, local short-time electromagnetic energy absorption rate, and local long-time electromagnetic energy absorption rate calculated in real time are compared with the safety thresholds pre-stored in the memory. If the global short-time electromagnetic energy absorption rate exceeds the global short-time threshold or the local short-time electromagnetic energy absorption rate exceeds the local short-time threshold, a termination scanning signal is sent to the multi-nucleoside synchronous imaging control spectrometer. Upon receiving the termination scanning signal, the multi-nucleoside synchronous imaging control spectrometer terminates the scanning process and prompts that the radio frequency energy of the multi-nucleoside synchronous imaging operation stage exceeds the limit and that the parameters need to be readjusted for scanning. If the global long-term electromagnetic energy absorption rate exceeds the global long-term threshold or the local long-term electromagnetic energy absorption rate exceeds the local long-term threshold, a pause scan signal is sent to the multi-nucleoside synchronous imaging control spectrometer. After receiving the pause scan signal, the multi-nucleoside synchronous imaging control spectrometer pauses scanning and waits for the pause scan signal of the multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit to become invalid before resuming scanning.

[0014] Furthermore, the electronic components of the plug-in radio frequency power measurement unit are all non-magnetic devices that do not interfere with the uniformity of the main magnetic field, and are encapsulated in a fully enclosed grounded aluminum shell to achieve electromagnetic interference protection.

[0015] Furthermore, the plug-in radio frequency power measurement unit supports multiplexing to radio frequency channels of different nuclides without changing the original radio frequency link structure of the multi-nucleus parallel MRI system. The number of plug-in radio frequency power measurement units is consistent with the total number of nuclide channels.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention fully considers the differences in the inherent resonant frequencies of different nuclides and uses the transmission line matrix method to calculate the electromagnetic energy absorption rate of multiple nuclides and multiple channels. In the transmission line matrix method, factors such as the frequency difference between nuclides and the phase difference between channels are injected into the scattering node as input conditions. The wave propagation, scattering and superposition process is automatically completed by the algorithm, and finally the total radio frequency energy field after superposition is obtained. This operation can increase the accuracy of the measured radio frequency electromagnetic energy absorption rate. 2. The present invention inserts the radio frequency power measurement unit into a multi-nucleoside parallel MRI system or a conventional MRI system as a plug-in, without changing the original radio frequency link of the system, without affecting the original imaging conditions, and has good practical performance. 3. The core components of this invention are designed in a modular manner, which ensures consistency between nuclides within the same MRI imaging system and between different systems. Before application, only a power meter is needed to calibrate the measurement error to achieve accurate measurement. The parameters between modules can be set by the multi-nucleus synchronous imaging operating table, such as the coil parameters. Any module can be portablely applied to single-core multi-channel and multi-core multi-channel parallel RF links. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the plug-in RF power measurement unit.

[0018] Figure 2 This is a schematic diagram of the structure of a digital signal processing unit for controlling the electromagnetic energy absorption rate of multiple nuclides.

[0019] Figure 3 This is a schematic diagram of the calculation and comparison process for the global electromagnetic energy absorption rate.

[0020] Figure 4 This is a flowchart illustrating the simulation calculation of local electromagnetic energy absorption rate.

[0021] Figure 5 This is a schematic diagram illustrating the interaction between a multi-nuclide parallel MRI system and a plug-in multi-nuclide multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system.

[0022] Notation: Plug-in RF power measurement unit 10, bidirectional directional coupler 11, true RMS response detector 12, fully differential amplifier 13, analog-to-digital conversion module 14, electro-optical conversion module 15, multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit 20, photoelectric conversion module 21, microprocessor 22, memory 23. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] In this embodiment, as Figures 1-5 As shown, this invention proposes a plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system. This system estimates the energy of radiofrequency radiation radiated to the subject by the subject by measuring the global and local short-term and long-term electromagnetic energy absorption rates of each nuclide and each radiofrequency link in real time, compares the results with safety thresholds, and controls the scanning process in real time to determine whether the scanning needs to be paused or terminated, thus avoiding irreversible harm to the subject.

[0025] Specifically, it includes several plug-in radio frequency power measurement units 10 and a set of multi-nucleoside electromagnetic energy absorption rate control digital signal processing units 20. The plug-in radio frequency power measurement unit 10 is inserted as an independent module into the radio frequency link of the multi-nucleoside parallel MRI system, that is, between the synchronous resonance / detuning switch and the multi-nucleoside parallel synchronous multi-channel coil unit. The multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit 20 is used to receive radio frequency power signals and calculate electromagnetic energy absorption rate, and interacts with the multi-nucleoside synchronous imaging control spectrometer to control the scanning process. The plug-in RF power measurement unit 10 includes a bidirectional directional coupler 11, a true RMS response detector 12, a fully differential amplifier 13, an analog-to-digital converter module 14, and an electro-optical converter module 15. The bidirectional directional coupler 11 is used to couple the forward and reflected power of different RF channels to the outside of the RF link. The true RMS response detector 12 is used to achieve high-precision RF power detection and output the power signal as a voltage signal. The fully differential amplifier 13 is used to calculate the difference between incident and reflected power and obtain the coil RF energy absorption rate of each nuclide and each channel. The analog-to-digital converter module 14 is used to convert analog signals into digital signals. The electro-optical converter module 15 is used to convert digital electrical signals into optical signals and transmit them to the multi-nuclide RF energy absorption rate control digital signal processing unit for processing. This plug-in RF power measurement unit 10 can be reused for other channels or other nuclides to obtain the RF electromagnetic energy absorption rate of each nuclide channel and transmit it to the multi-nuclide electromagnetic energy absorption rate control digital signal processing unit 20 for processing. The plug-in radio frequency power measurement unit 10 is installed on the side of the magnet near the coil. The multi-nucleoside radio frequency energy absorption rate control digital signal processing unit 20 is installed on the side of the multi-nucleoside multi-channel MRI imaging equipment near the multi-nucleoside synchronous imaging control spectrometer. The electro-optical conversion module 15 of the plug-in radio frequency power measurement unit 10 and the photoelectric conversion module 21 of the multi-nucleoside radio frequency energy absorption rate control digital signal processing unit 20 transmit optical signals through optical fiber and waveguides on the filter plate to avoid introducing interference.

[0026] Among them, such as Figure 2 As shown, the multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit 20 includes a photoelectric conversion module 21, a microprocessor 22, and a memory 23. The photoelectric conversion module 21 is used to convert the optical signal calculated by the plug-in radio frequency power measurement unit 10 into a digital electrical signal. The microprocessor 22 is used to calculate the estimated value of electromagnetic energy absorption rate based on the digital electrical signal sampled in real time, and compare it with the safety threshold accessed in real time by the memory 23, and send the corresponding scanning signal according to the comparison result.

[0027] Specifically, memory 23 uses DDR4 high-speed memory to meet the requirements of real-time access security thresholds. These security thresholds include the global long-time threshold (Tal), the global short-time threshold (Tas), the radio frequency power correction factors for each channel of each nuclide (Ea(i,j) and Eb(i,j)), and the gyromagnetic ratio of each nuclide (γ). i The system stores local long-term thresholds (Tpl) and local short-term thresholds (Tps) based on different locations. When the plug-in multi-nuclide multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system is initialized, it stores radio frequency radiation energy safety thresholds according to FDA and IEC regulations. The threshold data can be adjusted based on theoretical standards and actual needs, with long-term thresholds of 6 minutes and short-term thresholds of 10 seconds. Before MRI imaging begins, the multi-nuclide synchronous imaging control spectrometer sends the scanning location, coil number, and nuclide information to the multi-nuclide electromagnetic energy absorption rate control digital signal processing unit 20. The microprocessor 22 selects the corresponding local electromagnetic energy absorption rate safety thresholds Tpl and Tps in the memory 23 for different scanning areas, and selects the corresponding radio frequency power correction factors Ea(i,j) and Eb(i,j) in the memory 23 for different radio frequency imaging coils. The Ea(i,j) and Eb(i,j) of each coil are obtained through pre-experimental calculations and are obtained by fitting the measured values ​​of the plug-in radio frequency power measurement unit 10 for each channel of each nuclide to the actual measured values ​​of the power meter in the coil. The corresponding gyromagnetic ratio γ is selected according to the different nuclides used. i ; by 1 H / 19 F / 23 Na / 31Using four nuclides as representatives, the above-mentioned plug-in multi-nuclide multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system is used to monitor the electromagnetic energy absorption rate of MRI imaging. The scope of protection of this invention includes the above-mentioned nuclides, and the monitoring of electromagnetic energy absorption rate of MRI imaging for more or fewer nuclides. The structure and operation steps of each unit can be adjusted according to actual needs.

[0028] like Figure 1 As shown, the plug-in radio frequency power measurement unit 10 in this example includes a bidirectional directional coupler 11, two true RMS response detectors 12, a fully differential amplifier 13, an analog-to-digital converter module 14, and an electro-optical converter module 15. In a multi-nucleoside multi-channel MRI imaging device, the input and output terminals of the bidirectional directional coupler 11 are respectively connected to the nuclide. 1 H / 19 F / 23 Na / 31 P-synchronous resonance / detuning switch and 1 H / 19 F / 23 Na / 31 Between the P-type multi-nucleoside parallel synchronous coil units, a low-power signal with fixed power is coupled to measure the actual power. A true RMS response detector 12 is connected to the forward and reflective ends of a bidirectional directional coupler 11 to convert the power signal into an analog voltage signal. The outputs of the two true RMS response detectors 12 are then compared by a fully differential amplifier 13 to obtain the analog voltage signal. 1 H / 19 F / 23 Na / 31 The absorption power of each nuclide and each channel of the P-multi-nucleus parallel synchronous coil unit is converted from analog signal to digital signal using analog-to-digital converter module 14. The digital signal is then converted into optical signal by electro-optical converter module 15 and transmitted through optical fiber via waveguide mounted on filter plate to multi-nucleus electromagnetic energy absorption rate control digital signal processing unit 20.

[0029] like Figure 2 As shown, the multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit 20 in this example consists of a photoelectric conversion module 21, a microprocessor 22, and a memory 23. The photoelectric conversion module 21 converts the digital optical signal of radio frequency energy measured by the plug-in radio frequency power measurement unit 10 into a digital electrical signal that is directly processed by the microprocessor 22. The microprocessor 22 is responsible for receiving the radio frequency power measurement value in real time, calculating various real-time electromagnetic energy absorption rates, comparing them with the safety thresholds stored in the memory 23, controlling the scanning process, and sending a pause or termination signal to the multi-nucleoside synchronous imaging operation stage.

[0030] Among them, such as Figure 5As shown, the multi-nucleus parallel MRI system controls the radio frequency timing through a multi-nucleus synchronous imaging control spectrometer. It has multiple radio frequency links with identical structures but designed for different nuclides. The radio frequency excitation components of each nuclide's radio frequency link include a corresponding nuclide's radio frequency power amplifier, power divider, synchronous transmit / receive switch, synchronous resonance / detuning switch, plug-in radio frequency power measurement unit 10, and a multi-nucleus parallel synchronous multi-channel coil unit. The multi-nucleus synchronous imaging control spectrometer sends low-power radio frequency pulses of various frequencies and waveforms to the corresponding nuclide's radio frequency power amplifier. The high-power radio frequency signal, amplified by the radio frequency power amplifier, enters the radio frequency shielding chamber through a filter board. Each nuclide's high-power signal is divided into multiple channels with equal phase by a power divider. The high-power radio frequency pulse of each channel is fed into the multi-nucleus parallel synchronous multi-channel coil unit after passing through the synchronous transmit / receive switch and the synchronous resonance / detuning switch.

[0031] like Figure 5 As shown, the plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system in this example includes nuclides 1 H / 19 F / 23 Na / 31 Each of the four channels of the plug-in RF power measurement unit 10 and a set of multi-nucleus electromagnetic energy absorption rate control digital signal processing units 20, with each RF link of each nuclide containing a plug-in RF power measurement unit 10, inserting the nuclide. 1 H / 19 F / 23 Na / 31 P-synchronous resonance / detuning switch and 1 H / 19 F / 23 Na / 31 Between the P-type parallel synchronous coil units, the forward power and reverse power difference through the radio frequency channel are measured. The measurement results are digitized and converted into optical signals, which are sent in real time to the multi-nuclide electromagnetic energy absorption rate control digital signal processing unit 20. This unit calculates the real-time electromagnetic energy absorption rate of each nuclide and compares it with the stored safety threshold. If the safety threshold is exceeded, two real-time signals are sent to the multi-nuclide synchronous imaging control spectrometer to control the termination of the scanning process or to pause after the completion of this data acquisition, thereby realizing the safe control of radio frequency energy radiation of the subject during the multi-nuclide parallel imaging process.

[0032] Among them, such as Figure 4 As shown, the microprocessor 22 uses the transmission line matrix method (TLM) to perform real-time numerical simulation of the electric field energy distribution of the multi-nucleoside multi-channel radio frequency excitation source at each spatial node at each moment, and then calculates the local electromagnetic energy absorption rates Spl and Sps.

[0033] The process by which the microprocessor 22 calculates the local electromagnetic energy absorption rate includes: The entire three-dimensional space (including the coil, sample, and surrounding environment) for which the field distribution needs to be calculated is discretized into a grid R(m,n) composed of TLM nodes, and electromagnetic properties (dielectric constant ε and conductivity) are assigned to the nodes. And set the perfectly matched layer (PML) absorption boundary conditions at the grid boundary, define the source points corresponding to each radio frequency channel of each nuclide (i.e., which TLM nodes are excited), define the excitation signal (time domain waveform, such as a sine wave modulated Gaussian pulse, etc.) for each nuclide i and each channel j, set the frequency, amplitude ratio and phase difference between each signal, and establish the scattering matrix of the imaging area. After completing the initial condition setting, the time step iteration loop is entered. The time step N is set according to the total duration of multi-nucleus synchronous imaging. The excitation pulse S(i,j,t) of each nuclide and each channel is injected into the node. At each node, all incident pulses will arrive at the node center at the same time, simulating the reflection and interaction of electromagnetic waves on the medium node. The scattered pulses of the incident pulses at the adjacent nodes are simulated and calculated according to the scattering matrix of the imaging area. The pulse scattered by each node will become the incident pulse of the neighboring node in the next time step. Read the pulse voltage (V) and current (I) at grid position R(m,n), and calculate the corresponding electric field intensity E(R) according to the electric field intensity formula (as shown in Formula 1). When the time step has not reached the maximum value, calculate the local electromagnetic energy absorption rate Spt(m,n,t) at each moment according to the electromagnetic energy absorption rate formula (as shown in Formula 2). After averaging in the time domain, calculate the average electromagnetic energy Ssm(m,n,t) and Slm(m,n,t) at each grid position R(m,n) in the short time (10 seconds) and long time (6 minutes) respectively. Take the maximum value of Ssm(m,n,t) at all grid positions in the short time as the final result of the local short time electromagnetic energy absorption rate Sps(t), and take the maximum value of Slm(m,n,t) at all grid positions in the long time as the final result of the local long time electromagnetic energy absorption rate Spl(t).

[0034] Formula 1 is expressed as: Where U(R) is the voltage at grid position R(m,n), D(R) is the distance between the reference point and grid position R(m,n), and E(R) is the electric field intensity at spatial node R; Formula 2 is expressed as: ,in, The electrical conductivity of a local tissue. denoted as the density value of the local tissue, E(R) is the electric field value at the spatial node R, N is the number of channels of the same nuclide, and Spt is the local electromagnetic energy absorption rate.

[0035] Among them, such as Figure 3 As shown, the process by which the microprocessor 22 calculates the estimated electromagnetic energy absorption rate includes: The microprocessor 22 samples the radio frequency power sampling value P(i,j,t) from the plug-in radio frequency power measurement unit 10 of each nuclide and each channel, and corrects the radio frequency power sampling value P(i,j,t) by the corresponding radio frequency power correction factors Ea(i,j) and Eb(i,j).

[0036] Considering that the excitation radio frequency energy of each nuclide is proportional to the radio frequency pulse frequency (as shown in Equation 3), and the electromagnetic energy absorption rate is proportional to the square of the excitation radio frequency energy (as shown in Equation 4), and that under the same static magnetic field strength, the radio frequency pulse frequency is proportional to the gyromagnetic ratio, the correction factor needs to use the gyromagnetic ratio for each nuclide as the nuclide coefficient, and combine it with the radio frequency power correction factor to calculate the real-time electromagnetic energy absorption rate S(i,j,t) (as shown in Equation 5). The real-time electromagnetic energy absorption rate S(i,j,t) of each channel of each nuclide is shifted and buffered, and the buffer matrix is ​​sampled at the beginning, acquiring short-time (t=10 seconds) and long-time data. The real-time electromagnetic energy absorption rates Sts(i,j,t) and Stl(i,j,t) within t=6 minutes are averaged over time to obtain the short-time electromagnetic energy absorption rate Ssi(i,j,t) and the long-time electromagnetic energy absorption rate Sli(i,j,t), respectively. The short-time electromagnetic energy absorption rate Ssi(i,j,t) and the long-time electromagnetic energy absorption rate Sli(i,j,t) of each nuclide and each channel are weighted and summed to obtain the real-time estimation results of the global short-time electromagnetic energy absorption rate Sas(t) and the global long-time electromagnetic energy absorption rate Sal(t) of each nuclide and each channel. Formula 3 is expressed as: Where E is the root mean square value of the induced electric field intensity in the radiofrequency irradiated tissue, in V / m. is Planck's constant. The frequency of the radio frequency pulse; Formula 4 is expressed as: , where, The electrical conductivity of the radiofrequency irradiated tissue, expressed in S / m. Density of radiofrequency irradiated tissue, in kg / m³ 3 ; Formula 5 is expressed as: Where i is the nuclide number, j is the channel number, and i and j can both be 1, 2, 3, or 4, and t is the time number.

[0037] Among them, such as Figure 3 As shown, the process by which the microprocessor 22 sends the corresponding scan signal based on the comparison result includes: The global short-time electromagnetic energy absorption rate Sas(t), global long-time electromagnetic energy absorption rate Sal(t), local short-time electromagnetic energy absorption rate Sps(t), and local long-time electromagnetic energy absorption rate Spl(t) calculated in real time are compared with the safety thresholds pre-stored in memory 23. If the global short-time electromagnetic energy absorption rate Sas(t) exceeds the global short-time threshold (Tas) or the local short-time electromagnetic energy absorption rate Sps(t) exceeds the local short-time threshold (Tps), a termination scan signal is sent to the multi-nucleoside synchronous imaging control spectrometer. Upon receiving the termination scan signal, the multi-nucleoside synchronous imaging control spectrometer terminates the scanning process and prompts that the radio frequency energy of the multi-nucleoside synchronous imaging operation stage exceeds the limit and that the parameters need to be readjusted for scanning. If the global long-term electromagnetic energy absorption rate Sal(t) exceeds the global long-term threshold (Tal) or the local long-term electromagnetic energy absorption rate Spl(t) exceeds the local long-term threshold (Tpl), a pause scan signal is sent to the multi-nucleoside synchronous imaging control spectrometer. After receiving the pause scan signal, the multi-nucleoside synchronous imaging control spectrometer pauses scanning and waits for the pause scan signal of the multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit 20 to fail before continuing scanning.

[0038] Specifically, considering that multi-nuclide parallel MRI systems have multiple radio frequency excitation and acquisition frequencies, and that multi-nuclide radio frequency receiving links are very sensitive to electromagnetic interference (EMI) of various frequencies, robust EMI protection can prevent the plug-in radio frequency power measurement unit 10 from interfering with the multi-nuclide relaxation signal. Therefore, the electronic components of the plug-in radio frequency power measurement unit 10 in this invention are all non-magnetic devices that do not interfere with the uniformity of the main magnetic field, and are encapsulated in a fully enclosed grounded aluminum shell to achieve electromagnetic interference protection, thereby increasing the portability and versatility of the plug-in multi-nuclide multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system, reducing the analog signal transmission distance, and increasing the accuracy of signal measurement. Specifically, the plug-in radio frequency power measurement unit 10 supports multiplexing radio frequency channels to different nuclides without changing the original radio frequency link structure of the multi-nucleus parallel MRI system. The number of plug-in radio frequency power measurement units 10 is consistent with the total number of nuclide channels.

[0039] In summary, in this embodiment, the present invention proposes a plug-in multi-nuclide multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system. Without changing the original radio frequency link of the multi-nuclide parallel MRI system, the system inserts the radio frequency link in the form of a plug-in for measurement, filling the technical gap in electromagnetic energy absorption rate measurement of multi-nuclide parallel MRI systems and ensuring the personal safety of subjects during multi-nuclide imaging.

[0040] This invention measures the electromagnetic energy absorption rate of various nuclides using the pulse energy method. After calculating the local and global electromagnetic energy absorption rates of all nuclides, it compares them with safety thresholds. Local and global safety have equal priority, with short-term safety having higher priority than long-term safety. This can reasonably reduce the radiofrequency safety risk to subjects, enabling simultaneous in-situ imaging of all nuclides and precise monitoring of electromagnetic energy absorption rates, thus controlling the radiofrequency safety of the imaging process.

[0041] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system, characterized in that, It includes several plug-in radio frequency power measurement units and a set of multi-nucleoside electromagnetic energy absorption rate control digital signal processing units. The plug-in radio frequency power measurement units are inserted into the radio frequency link of the multi-nucleoside parallel MRI system in the form of plug-ins. The multi-nucleoside electromagnetic energy absorption rate control digital signal processing units are used to receive radio frequency power signals and calculate electromagnetic energy absorption rate, and interact with the multi-nucleoside synchronous imaging control spectrometer to control the scanning process. The plug-in RF power measurement unit includes a bidirectional directional coupler, a true RMS response detector, a fully differential amplifier, an analog-to-digital converter (ADC), and an electro-optical converter. The bidirectional directional coupler couples forward and reflected power from different RF channels to the outside of the RF link. The ADC enables high-precision RF power detection and outputs the power signal as a voltage signal. The fully differential amplifier calculates the difference between incident and reflected power and obtains the coil RF energy absorption rate for each nuclide and each channel. The ADC converts analog signals to digital signals, and the electro-optical converter converts digital electrical signals to optical signals, which are then transmitted to the multi-nuclide RF energy absorption rate control digital signal processing unit for processing. The plug-in radio frequency power measurement unit is installed on the side of the magnet near the coil. The multi-nuclide radio frequency energy absorption rate control digital signal processing unit is installed on the side of the multi-nuclide multi-channel MRI imaging device near the multi-nuclide synchronous imaging control spectrometer. The electro-optical conversion module of the plug-in radio frequency power measurement unit and the photoelectric conversion module of the multi-nuclide radio frequency energy absorption rate control digital signal processing unit transmit optical signals through optical fiber and waveguides on the filter board to avoid introducing interference.

2. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 1, characterized in that, The multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit includes a photoelectric conversion module, a microprocessor, and a memory. The photoelectric conversion module is used to convert the optical signal calculated by the plug-in radio frequency power measurement unit into a digital electrical signal. The microprocessor is used to calculate the estimated value of electromagnetic energy absorption rate based on the real-time sampled digital electrical signal, compare it with the safety threshold accessed in real time by the memory, and send the corresponding scanning signal according to the comparison result.

3. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 1, characterized in that, The multi-nucleus parallel MRI system controls the radio frequency timing through a multi-nucleus synchronous imaging control spectrometer. It contains multiple radio frequency links with identical structures but designed for different nuclides. Each nucleus's radio frequency link's radio frequency excitation component includes a corresponding nucleus's radio frequency power amplifier, power divider, synchronous transmit / receive switch, synchronous resonance / detuning switch, plug-in radio frequency power measurement unit, and a multi-nucleus parallel synchronous multi-channel coil unit. The multi-nucleus synchronous imaging control spectrometer sends low-power radio frequency pulses of various frequencies and waveforms to the corresponding nucleus's radio frequency power amplifier. The high-power radio frequency signal, amplified by the power amplifier, enters the radio frequency shielding chamber through a filter. Each nucleus's high-power signal is divided into multiple channels with equal phase by a power divider. The high-power radio frequency pulse of each channel is fed into the multi-nucleus parallel synchronous multi-channel coil unit after passing through the synchronous transmit / receive switch and the synchronous resonance / detuning switch.

4. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 2, characterized in that, The microprocessor uses the transmission line matrix method to perform real-time numerical simulation of the electric field energy distribution at each spatial node of a multi-nucleoside multi-channel radio frequency excitation source at each moment, and then calculates the local electromagnetic energy absorption rate.

5. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 4, characterized in that, The process by which the microprocessor calculates the local electromagnetic energy absorption rate includes: The entire three-dimensional space for calculating the field distribution is discretized into a grid composed of TLM nodes. Electromagnetic properties are assigned to the nodes and a perfectly matched layer absorption boundary condition is set at the grid boundary. The source point and excitation signal corresponding to each radio frequency channel of each nuclide are defined, and the scattering matrix of the imaging region is established. After completing the initial condition setting, the time step iteration loop is entered. The time step is set according to the total duration of multi-nucleus synchronous imaging. The excitation pulses of each nuclide and each channel are injected into the node. At each node, all incident pulses will arrive at the node center at the same time, simulating the reflection and interaction of electromagnetic waves on the medium node. The scattered pulses of the incident pulses at the adjacent nodes are simulated and calculated according to the scattering matrix of the imaging area. The pulses scattered by each node will become the incident pulses of the neighboring nodes in the next time step. The pulse voltage and current at the grid location are read, and the corresponding electric field intensity is calculated according to the electric field intensity formula. When the time step does not reach the maximum value, the local electromagnetic energy absorption rate at each moment is calculated according to the electromagnetic energy absorption rate formula. After averaging in the time domain, the average electromagnetic energy at each grid location in the short and long time periods is calculated respectively. The maximum value at all grid locations in the short time period is taken as the final result of the local short-time electromagnetic energy absorption rate, and the maximum value at all grid locations in the long time period is taken as the final result of the local long-time electromagnetic energy absorption rate.

6. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 5, characterized in that, The security thresholds include global long-time thresholds, global short-time thresholds, radio frequency power correction factors for each channel of each nuclide, magnetoresistive ratios of each nuclide, and local long-time thresholds and local short-time thresholds stored according to different locations.

7. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 6, characterized in that, The process by which the microprocessor calculates the estimated electromagnetic energy absorption rate includes: The microprocessor samples the radio frequency power (RF) values ​​from the plug-in RF power measurement units of each nuclide and each channel. It then corrects these RF power values ​​using a corresponding RF power correction factor. The gyromagnetic ratio for each nuclide is used as the nuclide coefficient. The real-time electromagnetic energy absorption rate is calculated using the RF power correction factor. The real-time RF energy absorption rate of each nuclide and each channel is shifted and buffered. The buffer matrix is ​​sampled at the beginning, and the real-time RF energy absorption rate is collected for both short and long-term periods. These are averaged over time to obtain the short-term and long-term RF energy absorption rates, respectively. The short-term and long-term RF energy absorption rates of each nuclide and each channel are then weighted and summed to obtain the real-time estimation results of the global short-term and global long-term RF energy absorption rates for each nuclide and each channel.

8. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 7, characterized in that, The process by which the microprocessor sends a corresponding scan signal based on the comparison result includes: The global short-time electromagnetic energy absorption rate, global long-time electromagnetic energy absorption rate, local short-time electromagnetic energy absorption rate, and local long-time electromagnetic energy absorption rate calculated in real time are compared with the safety thresholds pre-stored in the memory. If the global short-time electromagnetic energy absorption rate exceeds the global short-time threshold or the local short-time electromagnetic energy absorption rate exceeds the local short-time threshold, a termination scanning signal is sent to the multi-nucleoside synchronous imaging control spectrometer. Upon receiving the termination scanning signal, the multi-nucleoside synchronous imaging control spectrometer terminates the scanning process and prompts that the radio frequency energy of the multi-nucleoside synchronous imaging operation stage exceeds the limit and that the parameters need to be readjusted for scanning. If the global long-term electromagnetic energy absorption rate exceeds the global long-term threshold or the local long-term electromagnetic energy absorption rate exceeds the local long-term threshold, a pause scan signal is sent to the multi-nucleoside synchronous imaging control spectrometer. After receiving the pause scan signal, the multi-nucleoside synchronous imaging control spectrometer pauses scanning and waits for the pause scan signal of the multi-nucleoside electromagnetic energy absorption rate control digital signal processing unit to become invalid before resuming scanning.

9. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 1, characterized in that, The electronic components of the plug-in radio frequency power measurement unit are all non-magnetic devices that do not interfere with the uniformity of the main magnetic field, and are encapsulated in a fully enclosed grounded aluminum shell to achieve electromagnetic interference protection.

10. The plug-in multi-nucleoside multi-channel synchronous MRI real-time electromagnetic energy absorption rate monitoring system according to claim 1, characterized in that, The plug-in radio frequency power measurement unit supports multiplexing radio frequency channels to different nuclides without changing the original radio frequency link structure of the multi-nucleus parallel MRI system. The number of plug-in radio frequency power measurement units is consistent with the total number of nuclide channels.

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