Magnetic resonance radio frequency transmission system and method for magnetic resonance system radio frequency safety monitoring

Abstract

The application provides a magnetic resonance radio frequency transmitting system and a magnetic resonance system radio frequency safety monitoring method, wherein the forward power and / or the reverse power of each coil loop of a transmitting coil is measured through a directional coupler, the coupling current of each coil loop of the transmitting coil is measured through a coupling probe, and the power loss of the transmitting coil is determined according to the forward power, the reverse power and the coupling current of each coil loop, so that the specific absorption rate corresponding to a scanning sequence is determined, and the accuracy of radio frequency safety monitoring of the magnetic resonance radio frequency transmitting system is improved. In addition, the application solves the problem that the power loss of the transmitting coil in the magnetic resonance radio frequency transmitting system is difficult to measure due to the change of the transmitting amplitude and phase of each coil loop, and the real patient absorption power is more accurately obtained, so that the radio frequency safety of the patient in the super-high field multi-channel transmitting magnetic resonance system is ensured.

Description

Technical Field

[0001] This invention relates to the field of magnetic resonance imaging technology, and in particular to a magnetic resonance radio frequency transmission system and a method for radio frequency safety monitoring of a magnetic resonance system. Background Technology

[0002] Magnetic resonance imaging (MRI) is a high-tech imaging technique that uses the behavior of hydrogen nuclei in a magnetic field to create images. The physical basis of MRI is the resonance phenomenon related to the magnetism and magnetic field of matter; that is, the resonance characteristics exhibited by the interaction of radio frequency waves with a system possessing both angular momentum and magnetic moment in an external magnetic field. In clinical applications, it has become the gold standard for disease diagnosis in the central nervous system and also has unique advantages in the diagnosis of bone, joint, and soft tissue lesions. In recent years, ultra-high field MRI equipment has made rapid progress in areas such as magnetic resonance brain functional imaging, spectral imaging, white matter fiber tract imaging, and cardiac examinations due to its significant advantages, including superior spatial and temporal resolution and a better signal-to-noise ratio. In particular, the field strength of the main magnet in clinically applied MRI scanners has increased from below 0.2T to above 1.5T in recent years, and 3.0T ultra-high field MRI scanners have been certified and entered the clinical application stage.

[0003] High-field MRI imaging equipment offers numerous advantages, including increased proton magnetization, improved signal-to-noise ratio (SNR), shorter MRI signal acquisition time while maintaining SNR, enhanced chemical shift effect leading to improved resolution of metabolites in magnetic resonance spectroscopy (MRS), and increased blood oxygen saturation dependence effect, resulting in more pronounced signal changes in brain functional imaging. However, high-field and ultra-high-field MRI also present certain risks. Firstly, the complex anatomical structure of human tissues and organs, with significant differences in electromagnetic parameters and density across different tissues and organs, leads to varying attenuation of radiofrequency electromagnetic waves at different locations within the body. Secondly, as the main magnetic field strength increases, the corresponding Larmor resonance frequency also rises, shortening the wavelength of radiofrequency electromagnetic waves within the body. This results in a standing wave effect due to the superposition of incident and emitted electromagnetic waves during propagation. Both of these factors can affect the transmission of electromagnetic waves within the body, leading to excessive absorption of radiofrequency energy locally and a significant increase in the accumulated energy of high-field radiofrequency pulses. The specific absorption ratio (SAR), also known as the specific absorption rate problem, is particularly prominent in high-field magnetic resonance imaging (MRI) machines, especially in ultra-high field MRI imaging equipment with a field strength of 3.0T.

[0004] SAR (Specific Absorption and Response) refers to the electromagnetic power absorbed or consumed per unit mass of human tissue, expressed in watts per kilogram (W / kg). In magnetic resonance imaging (MRI) systems, the measurement of SAR values ​​is crucial for patient safety; the accuracy of SAR measurement directly impacts the assessment of the risk of burns to the patient.

[0005] In existing technologies, magnetic resonance imaging (MRI) systems measure the forward / reverse power of the coil units by placing directional couplers at the front end of the coils, calculating the net absorbed power of the system, and thus calculating the SAR value to ensure patient safety. However, since the net absorbed power of the system consists of two parts—one part is the power absorbed by the patient, and the other is the power loss of the coils—it is crucial to accurately measure the actual power loss of the coils. If the coil efficiency is high, the coil power loss can be ignored. However, in ultra-high field whole-body MRI systems, the efficiency of the body emission coils for whole-body scanning is generally low, and a considerable portion of the power is lost in the emission coils. Therefore, accurately measuring the actual power loss of the coils is extremely important. If the transmission modes (amplitude ratios and phase differences of each transmission channel) in a magnetic resonance imaging (MRI) system are relatively fixed, the coil power loss under a fixed transmission mode can be measured in advance. However, in ultra-high field multi-channel transmission systems, radio frequency symmetry is typically performed on the region of interest of the patient being scanned. After RF symmetry, the amplitude, phase, and even the transmission waveform of each RF channel change over time, resulting in a more uniform image. However, the coil power loss also varies significantly with the transmission waveform, amplitude ratio, and phase difference of each coil loop. Therefore, measuring the coil power loss under arbitrary amplitude, phase, and waveform conditions is difficult, and simultaneous measurement during scanning cannot separate the patient's absorbed power from the coil power loss. Therefore, it is necessary to propose a method to accurately monitor the patient's absorbed power in the MRI scanning area to ensure the patient's radio frequency safety in ultra-high field RF transmission MRI systems. Summary of the Invention

[0006] The purpose of this invention is to provide a magnetic resonance radio frequency transmission system and a method for monitoring the radio frequency safety of a magnetic resonance system, so as to accurately obtain the patient's absorbed power and ensure the radio frequency safety of the patient during scanning in an ultra-high field emission magnetic resonance system.

[0007] To achieve the above objectives, the present invention provides a magnetic resonance radio frequency transmission system, comprising:

[0008] A radio frequency generator is used to generate multiple sets of initial radio frequency pulse signals according to a scan sequence.

[0009] Multiple power amplifiers are connected to the radio frequency generator to amplify multiple sets of initial radio frequency pulse signals and transmit them to multiple transmission links respectively.

[0010] The transmitting coil contains multiple coil loops, each coil loop being connected to a transmission link;

[0011] Multiple directional couplers are correspondingly disposed between the power amplifier and the transmitting coil to measure the forward power and / or reverse power of each coil circuit;

[0012] Multiple coupling probes are used to measure the coupling current in each coil circuit; and

[0013] The data processing unit is used to acquire and / or process the forward power, the reverse power, and the coupling current of each coil circuit, and to determine the power loss of the transmitting coil based on the forward power, the reverse power, and the coupling current of each coil circuit.

[0014] Optionally, each coil loop may transmit an amplified initial radio frequency pulse signal independently in sequence; or, at least two coil loops may transmit linearly independent and amplified initial radio frequency pulse signals simultaneously.

[0015] Optionally, the data processing unit includes an analog-to-digital converter (ADC). The ADC acquires the first coupling signal output by the directional coupler corresponding to each coil circuit and the second coupling signal output by the coupling probe, and performs analog-to-digital conversion. The first coupling signal after analog-to-digital conversion is quadratured and used to determine the forward power or the reverse power. The second coupling signal after analog-to-digital conversion is quadratured and used to determine the coupling current.

[0016] Optionally, the data processing unit is further configured to determine the specific absorption rate corresponding to the scanning sequence based on the power loss of the transmitting coil.

[0017] Optionally, the magnetic resonance radio frequency transmission system further includes:

[0018] The controller is used to control the resonance or detuning of the transmitting coil according to the specific absorption rate corresponding to the scanning sequence, or to adjust the scanning sequence according to the specific absorption rate corresponding to the scanning sequence.

[0019] The present invention also provides a method for radio frequency safety monitoring of a magnetic resonance system, the magnetic resonance system including a transmitting coil, the transmitting coil comprising multiple coil loops, each coil loop being independently controllable to transmit radio frequency pulse signals, the method comprising:

[0020] The no-load power loss of the transmitting coil after executing the scanning sequence under no-load conditions and the no-load current factor of each coil loop of the transmitting coil are obtained respectively.

[0021] Under load, the transmitting coil is controlled to execute the scanning sequence to acquire the forward power, reverse power and coupling current of each coil circuit;

[0022] The on-load power loss of the transmitting coil and the on-load current factor of each coil circuit are determined based on the forward power, the reverse power and the coupling current of each coil circuit.

[0023] The power loss of the transmitting coil is determined based on the no-load power loss of the transmitting coil, the no-load current factor of each coil loop of the transmitting coil, and the on-load current factor.

[0024] The specific absorption rate corresponding to the scanning sequence is determined based on the on-load power loss and the power loss of the transmitting coil.

[0025] Optionally, controlling the transmitting coil to execute the scanning sequence under load includes:

[0026] According to the scanning sequence, the radio frequency pulse parameters are set for the transmitting coil;

[0027] According to the radio frequency pulse parameters, each coil circuit of the transmitting coil is controlled to transmit radio frequency pulse signals in sequence. When each coil circuit transmits radio frequency pulse signals, the forward power and / or reverse power of each coil circuit is measured using a directional coupler, and the coupling current of each coil circuit is measured using a coupling probe.

[0028] The forward and / or reverse power of each coil loop is used to determine the transmission matrix of the directional coupler;

[0029] The coupling current of each coil circuit is used to determine the transmission matrix of the coupling probe.

[0030] Optionally, controlling the transmitting coil to execute the scanning sequence under load includes:

[0031] According to the scanning sequence, radio frequency pulse parameters are set for the transmitting coil, and the radio frequency pulse parameters set for different coil loops of the transmitting coil satisfy a set relationship.

[0032] Based on the radio frequency pulse parameters, each coil loop of the transmitting coil is controlled to simultaneously transmit radio frequency pulse signals.

[0033] Optionally, controlling the transmitting coil to execute the scanning sequence under load includes:

[0034] According to the scanning sequence, radio frequency pulse parameters are set for the transmitting coil, wherein the radio frequency pulse parameters set for at least two coil loops of the transmitting coil are linearly independent or orthogonal;

[0035] Based on the radio frequency pulse parameters, control the at least two coil circuits to simultaneously transmit radio frequency pulse signals.

[0036] Optionally, the method further includes:

[0037] In response to the specific absorption rate corresponding to the scan sequence exceeding a set threshold, the radio frequency pulse parameters of the scan sequence are adjusted.

[0038] In summary, this invention provides a magnetic resonance radio frequency (MRRF) transmission system and a method for monitoring MRRF safety in such a system. It measures the forward and / or reverse power of each coil loop of the transmitting coil using a directional coupler, and measures the coupling current of each coil loop using a coupling probe. Based on the forward power, reverse power, and coupling current of each coil loop, the power loss of the transmitting coil is determined, thereby determining the specific absorption rate corresponding to the scan sequence. This improves the accuracy of MRRF safety monitoring in the MRRF transmission system. Furthermore, this invention solves the problem of difficulty in measuring the power loss of the transmitting coil in MRRF transmission systems as the amplitude and phase of each coil loop change, providing a more accurate estimate of the true absorbed power from the patient, thus ensuring the MR safety of the patient during scanning in an ultra-high field multi-channel transmitting MR system. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a magnetic resonance radio frequency transmission system provided in an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of a magnetic resonance radio frequency transmission system provided in an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram of the structure of the transmitting coil in a magnetic resonance radio frequency transmitting system according to an embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the coil circuit in the transmitting coil;

[0043] Figure 5 A flowchart of a radio frequency safety monitoring method for a magnetic resonance system provided in an embodiment of the present invention;

[0044] Figure 6 This is a schematic diagram of the coupling current of the coupling probe measuring coil circuit according to an embodiment of the present invention. Detailed Implementation

[0045] The magnetic resonance radio frequency transmission system and the radio frequency safety monitoring method for the magnetic resonance system of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description and drawings; however, it should be noted that the concept of the technical solution of the present invention can be implemented in many different forms and is not limited to the specific embodiments described herein. The accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0046] The terms "first," "second," etc., used in this specification are used to distinguish between similar elements and are not necessarily used to describe a specific order or chronological sequence. It should be understood that these terms, used so in this way, may be replaced where appropriate, for example, to allow embodiments of the invention described herein to operate in a different order than that described or shown herein. Similarly, if the methods described herein comprise a series of steps, and the order of these steps presented herein is not necessarily the only possible order in which these steps can be performed, and some described steps may be omitted and / or some other steps not described herein may be added to the method. If a component in one figure is identical to a component in another figure, although these components are readily identifiable in all figures, this specification will not label all identical components in every figure for the sake of clarity.

[0047] Figure 1 This is a schematic diagram of the magnetic resonance radio frequency transmission system provided in this embodiment. Figure 2 This is a schematic diagram of the magnetic resonance radio frequency transmission system provided in this embodiment, as shown below. Figure 1 and Figure 2 As shown, the magnetic resonance radio frequency transmission system provided in this embodiment includes:

[0048] A radio frequency generator is used to generate multiple sets of initial radio frequency pulse signals according to a scan sequence.

[0049] Multiple power amplifiers are connected to the radio frequency generator to amplify multiple sets of initial radio frequency pulse signals and transmit them to multiple transmission links respectively.

[0050] The transmitting coil contains multiple coil loops, each coil loop is connected to a transmission link, and each coil loop is used to transmit an amplified initial radio frequency pulse signal;

[0051] Multiple directional couplers are correspondingly disposed between the power amplifier and the transmitting coil to measure the forward power and / or reverse power of each coil circuit;

[0052] Multiple coupling probes are used to measure the coupling current in each coil circuit; and

[0053] The data processing unit is used to collect and process the forward power, the reverse power, and the coupling current of each coil circuit, and to determine the power loss of the transmitting coil based on the forward power, the reverse power, and the coupling current of each coil circuit.

[0054] Specifically, such as Figure 1 As shown, the radio frequency generator (RF generator) in the magnetic resonance RF transmission system provided in this embodiment Figure 1(Not shown in the image), multiple initial radio frequency (RF) pulse signals are generated according to the scanning sequence. Power amplifiers 1, 2, ..., n, located on each transmission link, respectively convert the multiple initial RF pulse signals generated by the RF generator into signals. The signal is amplified and transmitted to multiple transmission links to form a radio frequency (RF) field, where n is the number of transmission links. The RF fields generated by the multiple transmitting coils are spatially superimposed to form the desired uniform RF field in the region of interest. Here, H represents the conjugate transpose of a matrix. The transmission links also include capacitors and inductors connected to the transmitting coils, forming coil unit 1, coil unit 2, ..., coil unit n, where n is an integer greater than 1.

[0055] In this embodiment, each coil circuit independently transmits an amplified initial radio frequency pulse signal in sequence, or at least two coil circuits simultaneously transmit linearly independent and amplified initial radio frequency pulse signals.

[0056] Figure 3 This is a schematic diagram of the transmitting coil in the magnetic resonance radio frequency transmitting system provided in this embodiment. Figure 4 This is a schematic diagram of the coil circuit in the transmitting coil. (For example...) Figure 3 and Figure 4 As shown, the transmitting coil (RF coil) may include multiple crossbars and two ends. Each crossbar has a horizontal end antenna, and each end has an end loop antenna. Ends are located at both ends of the crossbars and at the ends between adjacent crossbars, and the crossbars are connected to their respective ends. Multiple crossbars are arranged at circumferential intervals (preferably uniformly spaced) along the transmitting coil, and extend along the axial direction of the transmitting coil. Each crossbar includes multiple crossbar sub-units arranged sequentially adjacent to each other along the axial direction of the transmitting coil. Adjacent crossbar units are connected by capacitors. Typically, two adjacent crossbar units located in the middle of a crossbar are connected by a fixed capacitor, while two crossbar units near the ends of a crossbar, or crossbar units connected to the ends, are connected by adjustable capacitors (i.e., the capacitance value of the capacitor can be adjusted). This arrangement allows the error of each fixed capacitor to be adjusted by the adjustable capacitor, thereby achieving accurate transmitting frequency calibration. In addition, each end includes multiple end sub-units, which are arranged at intervals along the circumference of the transmitting coil to form a ring-shaped end.

[0057] In this embodiment, two adjacent crossbars together with multiple end subunits located between the two crossbars form a coil loop (LOOP). It can be seen that the transmitting coil includes multiple coil loops arranged circumferentially, and the number of coil loops is equal to the number of crossbars of the transmitting coil.

[0058] In this embodiment, directional couplers 1, 2, ..., n are installed between the power amplifier and the transmitting coil (on the input side of the transmitting coil) on each transmission link. Transmission characteristics are measured on each transmission link, and a first coupling signal is output to measure the forward power PF1, PF2, ..., PFn of each coil loop. n and the reverse power PR1, forward power PR2, ..., forward power PR of each coil circuit. n In addition, coupling probes 1, 2, ..., n are respectively installed on each transmission link within a preset near-field radiation distance of the transmitting coil. These probes are positioned within the preset near-field radiation distance of the transmitting coil to measure the transmission characteristics of each coil loop, output a second coupling signal, and measure the coupling current I generated by the transmitting coil in each coil loop. probe1 Coupling current I probe2 , ..., coupling current I proben .

[0059] It should be noted that in this embodiment, the power loss of the transmitting coil is calculated by measuring the coupling current of each coil circuit using a coupling probe. In other embodiments of the present invention, the power loss of the transmitting coil can also be calculated by measuring the coupling magnetic field or other parameters of each coil circuit using a coupling probe. The present invention does not impose any limitations on this.

[0060] The data processing unit includes an analog-to-digital converter (A / D). The forward coupling terminal (PF) and reverse coupling terminal (PR) of the directional couplers on each transmission link are connected to the A / D converter. A coupling probe is connected to the A / D converter via a transmission line. The A / D converter acquires the first coupling signal output by the directional coupler corresponding to each coil circuit and the second coupling signal output by the coupling probe, and performs analog-to-digital conversion. The first coupling signal after analog-to-digital conversion is quadrature demodulated and used to determine the forward power or the reverse power. The second coupling signal after analog-to-digital conversion is quadrature demodulated and used to determine the coupling current.

[0061] The data processing unit is also used to determine the specific absorption rate (SAR) corresponding to the scanning sequence based on the power loss of the transmitting coil. For example, during system adjustment or maintenance, multiple measurements are first performed on the transmitting coil under no-load conditions. Based on the coupling of these multiple measurements, the no-load power loss of the transmitting coil after executing the scanning sequence under no-load conditions and the no-load current factor of each coil loop are obtained. Then, when scanning the patient, measurements are performed on the transmitting coil under loaded conditions. Based on the measured forward power, reverse power, and coupling current of each coil loop, the loaded power loss of the transmitting coil and the loaded current factor of each coil loop are determined, combined with the no-load power loss under no-load conditions. The power loss of the transmitting coil under loaded conditions is related to both the current measurements under loaded conditions and the transmission matrix during system adjustment. The patient's absorbed power equals the net absorbed power minus the coil power loss under loaded conditions. Then, the patient's absorbed power is calculated to obtain the SAR absorbed by the patient over a certain average time, ensuring that the patient's absorbed SAR does not exceed the standard limit.

[0062] The multi-channel magnetic resonance radio frequency transmission system provided in this embodiment also includes a controller, used to control the resonance or detuning of the transmission coil according to the specific absorption rate corresponding to the scanning sequence, or to adjust the scanning sequence according to the specific absorption rate corresponding to the scanning sequence. Correspondingly, when the patient's absorbed SAR is detected to exceed the standard limit, the data processing unit feeds back the result to the controller in the magnetic resonance radio frequency transmission system to adjust the resonance or detuning of the transmission coil accordingly, or to adjust the scanning sequence, and issues a corresponding alarm, thereby achieving monitoring of the radio frequency safety of the magnetic resonance radio frequency transmission system.

[0063] In the magnetic resonance radio frequency (RF) transmission system provided in this embodiment, an RF generator generates multiple sets of initial RF pulse signals according to a scanning sequence; multiple power amplifiers are connected to the RF generator, amplifying the multiple sets of initial RF pulse signals and transmitting them to multiple transmission links respectively; a transmitting coil includes multiple coil loops, each coil loop connected to a transmission link, and each coil loop is used to transmit the amplified initial RF pulse signal; multiple directional couplers are correspondingly disposed between the power amplifiers and the transmitting coil to measure the forward and / or reverse power of each coil loop; multiple coupling probes measure the coupling current of each coil loop; and a data processing unit determines the power loss of the transmitting coil based on the forward power, reverse power, and coupling current of each coil loop. In the magnetic resonance RF transmission system provided in this embodiment, the forward and / or reverse power of each coil loop of the transmitting coil is measured by directional couplers, the coupling current of each coil loop of the transmitting coil is measured by coupling probes, and the power loss of the transmitting coil is determined based on the forward power, reverse power, and coupling current of each coil loop, thereby determining the specific absorption rate corresponding to the scanning sequence and improving the accuracy of RF safety monitoring of the magnetic resonance RF transmission system. In addition, this embodiment solves the problem of difficulty in measuring the power loss of the transmitting coil in the magnetic resonance radio frequency transmitting system as the transmitting amplitude and phase of each coil circuit change, and obtains the true absorbed power of the patient more accurately, thereby ensuring the radio frequency safety of the patient during scanning in the ultra-high field multi-channel transmitting magnetic resonance system.

[0064] Accordingly, this embodiment also provides a radio frequency safety monitoring method for a magnetic resonance system. The magnetic resonance system includes a transmitting coil, which comprises multiple coil loops, each of which can be independently controlled to transmit radio frequency pulse signals, such as... Figure 6 As shown, the method includes:

[0065] Step S01: Obtain the no-load power loss of the transmitting coil after performing the scanning sequence under no-load conditions, and the no-load current factor of each coil loop of the transmitting coil;

[0066] Step S02: Under load, control the transmitting coil to execute the scanning sequence to collect the forward power, reverse power and coupling current of each coil circuit;

[0067] Step S03: Determine the on-load power loss of the transmitting coil and the on-load current factor of each coil circuit based on the forward power, the reverse power and the coupling current of each coil circuit.

[0068] Step S04: Determine the power loss of the transmitting coil based on the no-load power loss of the transmitting coil, the no-load current factor of each coil loop of the transmitting coil, and the on-load current factor;

[0069] Step S05: Determine the specific absorption rate corresponding to the scanning sequence based on the on-load power loss of the transmitting coil and the power loss of the transmitting coil.

[0070] Optionally, after determining the specific absorption rate corresponding to the scan sequence, it is determined whether the specific absorption rate corresponding to the scan sequence is within a set threshold range. In response to the specific absorption rate corresponding to the scan sequence exceeding the set threshold, the radio frequency pulse parameters of the scan sequence are adjusted.

[0071] Optionally, the no-load power loss of the transmitting coil is determined by the forward power, reverse power, and coupling current of each coil circuit collected after the transmitting coil performs a scanning sequence under no-load conditions; the no-load current factor of each coil circuit is determined by the coupling current of each coil circuit collected after the transmitting coil performs a scanning sequence under no-load conditions.

[0072] Optionally, controlling the transmitting coil to execute the scanning sequence under load includes:

[0073] According to the scanning sequence, the radio frequency pulse parameters are set for the transmitting coil;

[0074] According to the radio frequency pulse parameters, each coil circuit of the transmitting coil is controlled to transmit radio frequency pulse signals in sequence. When each coil circuit transmits radio frequency pulse signals, the forward power and / or reverse power of each coil circuit is measured using a directional coupler, and the coupling current of each coil circuit is measured using a coupling probe.

[0075] The forward and / or reverse power of each coil loop is used to determine the transmission matrix of the directional coupler;

[0076] The coupling current of each coil circuit is used to determine the transmission matrix of the coupling probe.

[0077] Optionally, controlling the transmitting coil to execute the scanning sequence under load includes:

[0078] According to the scanning sequence, radio frequency pulse parameters are set for the transmitting coil, and the radio frequency pulse parameters set for different coil loops of the transmitting coil correspond to the set amplitude ratio or phase difference;

[0079] Based on the radio frequency pulse parameters, each coil loop of the transmitting coil is controlled to simultaneously transmit radio frequency pulse signals.

[0080] Optionally, controlling the transmitting coil to execute the scanning sequence under load includes:

[0081] According to the scanning sequence, radio frequency pulse parameters are set for the transmitting coil, wherein the radio frequency pulse parameters set for at least two coil loops of the transmitting coil are linearly independent or orthogonal;

[0082] Based on the radio frequency pulse parameters, control the at least two coil circuits to simultaneously transmit radio frequency pulse signals.

[0083] Next, we will take the example of each coil circuit independently transmitting amplified initial radio frequency pulse signals in sequence to introduce in detail the radio frequency safety monitoring method of the magnetic resonance system.

[0084] First, the no-load power loss of the transmitting coil after performing the scanning sequence under no-load conditions and the no-load current factor of each coil loop of the transmitting coil are obtained respectively.

[0085] For example, during equipment installation or maintenance, transmission characteristics are measured using a directional coupler and coupling probe under no-load conditions (without a phantom or with a low-loss phantom placed within the scanning aperture). This could involve each coil circuit sequentially and individually transmitting its first radio frequency pulse signal. That is, the first measurement involves transmitting the first radio frequency pulse signal to the first coil circuit. At that time, the forward power PF of the n-channel directional coupler is collected. unload_11 PF unload_21 , ..., PF unload_n1 Reverse power PR unload_11 PR unload_21 , ...,PR unload_n1 The coupling current Iprobe of the coupling probe unload_11 Iprobe unload_21 ..., Iprobe unload_n1 The second measurement involved transmitting the first radio frequency pulse signal through the second coil circuit. At that time, the forward power PF of the n-channel directional coupler is collected. unload_12 PF unload_22 , ..., PF unload_n2 Reverse power PR unload_12 PR unload_22 , ...,PR unload_n2 The coupling current Iprobe of the coupling probe unload_12 Iprobe unload_22 ..., Iprobe unload_n2 Similarly, the nth measurement involves the nth coil circuit transmitting the first radio frequency pulse signal. At that time, the forward power PF of the n-channel directional coupler is collected. unload_1n PF unload_2n , ..., PF unload_nn Reverse power PR unload_1n PR unload_2n , ...,PRunload_nn The coupling current Iprobe of the coupling probe unload_1n Iprobe unload_2n ..., Iprobe unload_nn In the above-mentioned forward power, reverse power, and coupling current, the first subscript represents the coil circuit number corresponding to the directional coupler or coupling probe, and the second subscript represents the coil circuit number corresponding to the transmitted radio frequency pulse signal being detected.

[0086] In one embodiment, the coupling probe can detect the unloaded coupling current or the loaded coupling current after scanning sequence excitation, under either unloaded or loaded conditions. Let the radio frequency current passing through the conductor be I. According to Biot-Savart's law, the magnetic field generated at point P satisfies the following relationship: Where μ0 is the free permeability and is constant; dl is a tiny line element of the radio frequency current; and r represents the distance between the conductor and point P. From the above equation, it can be seen that the magnetic field B generated by the radio frequency current I at point P is directly proportional to the current flowing through it and inversely proportional to the square of the distance r. (See attached...) Figure 6 As shown in the schematic diagram of the coupling current measurement coil circuit provided in an embodiment of the present invention, a current probe coupling loop is placed at point P around each coil circuit of the radio frequency coil as the coupling probe. The area of ​​the current probe coupling loop is A. Then the voltage V induced by the current probe coupling loop is... loop Magnetic flux of the coupling loop with the current probe Related, that is Assuming that the magnetic field B is uniform within area A, the voltage coupled by the current probe coupling loop is: Therefore, the voltage V coupled to the current probe coupling loop loop It is proportional to the radio frequency current I. Therefore, by mathematically transforming the coupling amount of the current probe coupling loop, the coupling current of the coil circuit can be obtained.

[0087] Based on the aforementioned forward power, reverse power, and coupling current, the transmission matrices of the forward power, reverse power, and coupling current with the first RF pulse signal under no-load conditions are obtained. Specifically, the transmission matrix M1 of the forward power of each coil circuit with the first RF pulse signal under no-load conditions is as follows:

[0088]

[0089] Under no-load conditions, the reverse power of each coil circuit and the transmission matrix M2 of the first radio frequency pulse signal are:

[0090]

[0091] Under no-load conditions, the coupling current of each coil circuit and the transmission matrix M3 of the first radio frequency pulse signal are:

[0092]

[0093] in, P is the first radio frequency pulse signal sequentially transmitted by each coil circuit under no-load conditions. Funload_nn PR represents the forward power of the nth coil circuit under no-load conditions during the nth measurement. unload_nn Iprobe represents the reverse power of the nth coil circuit under no-load conditions during the nth measurement. unload_nn This represents the coupling current of the transmitting coil in the nth coil circuit during the nth measurement under no-load conditions.

[0094] Next, under load, the transmitting coil is controlled to execute the scanning sequence to acquire the forward power, reverse power and coupling current of each coil circuit.

[0095] The forward power of each coil circuit under load and the transmission matrix M4 of the first radio frequency pulse signal are as follows:

[0096]

[0097] The reverse power of each coil circuit under load and the transmission matrix M5 of the first radio frequency pulse signal are as follows:

[0098]

[0099] Under load conditions, the coupling current of each coil circuit and the transmission matrix M6 of the first radio frequency pulse signal are:

[0100]

[0101] in, PF is the first radio frequency pulse signal sequentially transmitted by each coil circuit under load conditions. load_nn Let PR be the forward power of the nth coil circuit under load during the nth measurement. load_nn Iprobe represents the reverse power of the nth coil circuit under load during the nth measurement. load_nn Let be the coupling current of the transmitting coil of the nth coil circuit under load during the nth measurement.

[0102] In this embodiment, before obtaining the transmission matrix M1, transmission matrix M2, transmission matrix M3, transmission matrix M4, transmission matrix M5, and transmission matrix M6 respectively, the method further includes performing analog-to-digital conversion on the first coupling signal output by the directional coupler and the second coupling signal output by the coupling probe under no-load and loaded conditions respectively. The first coupling signal after analog-to-digital conversion is orthogonally demodulated to obtain the real / imaginary part or amplitude / phase information of the first coupling signal and the second coupling signal respectively, so as to obtain the forward power, the reverse power, and the coupling current of each coil circuit under no-load and loaded conditions.

[0103] Next, the on-load power loss of the transmitting coil and the on-load current factor of each coil circuit are determined based on the forward power, the reverse power and the coupling current of each coil circuit.

[0104] The radio frequency generator generates multiple sets of second radio frequency pulse signals according to the current scan sequence. These signals are amplified by multiple power amplifiers and sent to multiple transmit coils to form a second radio frequency field. Using the aforementioned measurements, the transmission matrices M1, M2, M3, M4, M5, and M6 are used to calculate the patient's specific absorption rate (SAR) by performing the following steps. This ensures that the patient's absorbed SAR does not exceed the standard limit, thereby ensuring the radio frequency safety of the patient during scanning in the ultra-high field multi-channel transmit magnetic resonance imaging system.

[0105] Specifically, based on the second radio frequency pulse signal of each coil circuit Given the amplitude and phase, calculate the no-load power loss (Coil_loss) of the transmitting coil under no-load conditions. unload and the no-load current factor Iprobe of the transmitting coil unload The calculation method is as follows:

[0106]

[0107]

[0108]

[0109]

[0110]

[0111] Among them, [PF unload_1 PF unload_2 , ..., PF unload_n ] H For the forward power of each coil circuit under no-load conditions during the transmission of the second radio frequency pulse signal, [PR unload_1 PR unload_2, ..., PR unload_n ] H This represents the reverse power of each coil circuit under no-load conditions when the second radio frequency pulse signal is transmitted. This represents the coupling current of each coil loop under no-load conditions during the transmission of the second radio frequency pulse signal, where n is the number of coil loops, and the superscript H represents the transpose of the row vector; 2 This indicates the operation of finding the 2-norm.

[0112] Next, based on the second radio frequency pulse signal of each coil circuit Given the amplitude and phase, calculate the power loss (net absorbed power) of each coil circuit under loaded conditions. load The on-load power loss (Coil_loss) of the transmitting coil load and the on-load current factor Iprobe of the transmitting coil load The calculation method is as follows:

[0113]

[0114]

[0115]

[0116] In this embodiment, the power loss of each coil loop under load (power loss of the transmitting coil) is the sum of the mean square differences between the forward and reverse power of each loop under load. The on-load current factor Iprobe of the transmitting coil... load This is the sum of the L2 norms of all coil circuits under load.

[0117]

[0118]

[0119] Based on the no-load power loss of the transmitting coil, the no-load current factor of each coil loop of the transmitting coil, and the on-load current factor, the power loss of the transmitting coil (on-load power loss Coil_loss) can be determined. load ).

[0120]

[0121] Among them, [PF load_1 PF load_2 , ..., PF load_n ] H For the forward power of each coil circuit under load conditions during the transmission of the second radio frequency pulse signal, [PR load_1 PR load_2 , ..., PR load_n ]H The reverse power of each coil circuit under load conditions during the transmission of the second radio frequency pulse signal, [Iprobe] load_1 Iprobe load_2 ..., Iprobe load_n ] H This represents the coupling current of each coil circuit under load when the second radio frequency pulse signal is transmitted, where n is the number of transmitting coils, and the superscript H represents the transpose of the row vector.

[0122] Next, calculate the patient's absorbed power. patient To obtain the patient's specific absorbance SAR, the specific calculation method is as follows:

[0123] Power patient =Net_Power load -Coil_loss load ;

[0124]

[0125] Where Mass is used to calculate the quality of the SAR, and t is used to calculate the average time of the SAR or the excitation time of the radio frequency pulse for the patient.

[0126] In the calculation of the specific absorption rate (SAR) of the above patients, the changes in coil power loss in the magnetic resonance radio frequency transmission system with the phase of the transmission amplitude of each coil circuit were taken into account, so as to obtain the true absorption power of the patient more accurately and thus ensure the radio frequency safety of the patient during scanning in the ultra-high field multi-channel transmission magnetic resonance system.

[0127] The radio frequency pulse parameters set for different coil loops of the transmitting coil can satisfy the set relationship. In other embodiments of the present invention, if the system keeps the amplitude ratio and phase difference of the radio frequency signals generated by each coil loop unchanged within a scanning time, the case of the first radio frequency pulse signal and the second radio frequency pulse signal under load in the above-mentioned radio frequency safety monitoring method can be simplified to not performing single coil loop excitation, but directly performing one excitation and measurement according to the amplitude ratio and phase difference of the radio frequency signals of each coil loop. The measurement under load can directly use the forward power, reverse power and coupling current of each coil loop, without needing to calculate and synthesize through the loaded transmission matrix.

[0128] In summary, this invention provides a magnetic resonance radio frequency (RF) transmission system and a method for monitoring the RF safety of the RF system, comprising: an RF generator generating multiple sets of initial RF pulse signals according to a scanning sequence; multiple power amplifiers connected to the RF generator, amplifying the multiple sets of initial RF pulse signals and transmitting them to multiple transmission links respectively; a transmitting coil comprising multiple coil loops, each coil loop being connected to a transmission link and each coil loop being used to transmit the amplified initial RF pulse signal; multiple directional couplers correspondingly disposed between the power amplifiers and the transmitting coil, measuring the forward power and / or reverse power of each coil loop; multiple coupling probes measuring the coupling current of each coil loop; and a data processing unit determining the power loss of the transmitting coil based on the forward power, the reverse power, and the coupling current of each coil loop. The magnetic resonance radio frequency (MRRF) transmission system provided by this invention measures the forward and / or reverse power of each coil loop of the transmitting coil using a directional coupler, and measures the coupling current of each coil loop using a coupling probe. Based on the forward power, reverse power, and coupling current of each coil loop, the power loss of the transmitting coil is determined, thereby determining the specific absorption rate corresponding to the scan sequence. This improves the accuracy of RF safety monitoring in the MRRF transmission system. Furthermore, this invention solves the problem of difficulty in measuring the power loss of the transmitting coil in MRRF transmission systems as the transmission amplitude and phase of each coil loop change, providing a more accurate estimate of the true patient absorbed power and ensuring RF safety for patients scanning in ultra-high field multi-channel transmitting MR systems.

[0129] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A magnetic resonance radio frequency transmission system, characterized in that, include: A radio frequency generator is used to generate multiple sets of initial radio frequency pulse signals according to a scan sequence. Multiple power amplifiers are connected to the radio frequency generator to amplify multiple sets of initial radio frequency pulse signals and transmit them to multiple transmission links respectively. The transmitting coil contains multiple coil loops, each coil loop is connected to a transmission link, and each coil loop can be independently controlled to transmit radio frequency pulse signals. Multiple directional couplers are correspondingly disposed between the power amplifier and the transmitting coil to measure the forward power and / or reverse power of each coil circuit; Multiple coupling probes are positioned within a preset near-field radiation distance of the transmitting coil to measure the coupling current of each coil circuit. as well as The data processing unit is used to acquire, respectively, the no-load power loss of the transmitting coil after executing the scanning sequence under no-load conditions and the no-load current factor of each coil loop of the transmitting coil, and, under loaded conditions during the execution of the scanning sequence, to acquire and process the forward power, the reverse power and the coupling current of each coil loop to obtain the loaded power loss of the transmitting coil and the loaded current factor of each coil loop, and to determine the power loss of the transmitting coil as the transmission amplitude and phase of each coil loop changes during the execution of the scanning sequence based on the no-load power loss of the transmitting coil, the no-load current factor of each coil loop of the transmitting coil and the loaded current factor.

2. The magnetic resonance radio frequency transmission system according to claim 1, characterized in that, Each coil circuit independently transmits an amplified initial radio frequency pulse signal in sequence; or, at least two coil circuits simultaneously transmit linearly independent and amplified initial radio frequency pulse signals.

3. The magnetic resonance radio frequency transmission system according to claim 1, characterized in that, The data processing unit includes an analog-to-digital converter (ADC). The ADC acquires the first coupling signal output by the directional coupler corresponding to each coil circuit and the second coupling signal output by the coupling probe, and performs analog-to-digital conversion. The first coupling signal after analog-to-digital conversion is used to determine the forward power or the reverse power after quadrature demodulation. The second coupling signal after analog-to-digital conversion is used to determine the coupling current after quadrature demodulation.

4. The magnetic resonance radio frequency transmission system according to claim 3, characterized in that, The data processing unit is also used to determine the specific absorption rate corresponding to the scanning sequence based on the power loss of the transmitting coil.

5. The magnetic resonance radio frequency transmission system according to claim 4, characterized in that, Also includes: A controller is used to control the resonance or detuning of the transmitting coil according to the specific absorption rate corresponding to the scanning sequence, or to adjust the scanning sequence according to the specific absorption rate corresponding to the scanning sequence.

6. A method for radio frequency safety monitoring of a magnetic resonance system, the magnetic resonance system comprising a transmitting coil, the transmitting coil comprising multiple coil loops, each coil loop being independently controllable to transmit radio frequency pulse signals, characterized in that, The method includes: The no-load power loss of the transmitting coil after executing the scanning sequence under no-load conditions and the no-load current factor of each coil loop of the transmitting coil are obtained respectively. Under load, the transmitting coil is controlled to execute the scanning sequence to acquire the forward power, reverse power and coupling current of each coil circuit; The on-load power loss of the transmitting coil and the on-load current factor of each coil circuit are determined based on the forward power, the reverse power and the coupling current of each coil circuit. The power loss of the transmitting coil is determined based on the no-load power loss of the transmitting coil, the no-load current factor of each coil loop of the transmitting coil, and the on-load current factor. The specific absorption rate corresponding to the scanning sequence is determined based on the on-load power loss and the power loss of the transmitting coil.

7. The radio frequency safety monitoring method for a magnetic resonance system according to claim 6, characterized in that, The step of controlling the transmitting coil to execute the scanning sequence under load includes: According to the scanning sequence, the radio frequency pulse parameters are set for the transmitting coil; According to the radio frequency pulse parameters, each coil circuit of the transmitting coil is controlled to transmit radio frequency pulse signals in sequence. When each coil circuit transmits radio frequency pulse signals, the forward power and / or reverse power of each coil circuit is measured using a directional coupler, and the coupling current of each coil circuit is measured using a coupling probe. The forward and / or reverse power of each coil loop is used to determine the transmission matrix of the directional coupler; The coupling current of each coil circuit is used to determine the transmission matrix of the coupling probe.

8. The radio frequency safety monitoring method for a magnetic resonance system according to claim 6, characterized in that, The step of controlling the transmitting coil to execute the scanning sequence under load includes: According to the scanning sequence, radio frequency pulse parameters are set for the transmitting coil, and the radio frequency pulse parameters set for different coil loops of the transmitting coil satisfy a set relationship. Based on the radio frequency pulse parameters, each coil loop of the transmitting coil is controlled to simultaneously transmit radio frequency pulse signals.

9. The radio frequency safety monitoring method for a magnetic resonance system according to claim 6, characterized in that, The step of controlling the transmitting coil to execute the scanning sequence under load includes: According to the scanning sequence, radio frequency pulse parameters are set for the transmitting coil, wherein the radio frequency pulse parameters set for at least two coil loops of the transmitting coil are linearly independent or orthogonal; Based on the radio frequency pulse parameters, control the at least two coil circuits to simultaneously transmit radio frequency pulse signals.

10. The radio frequency safety monitoring method for a magnetic resonance system according to any one of claims 6-9, characterized in that, The method further includes: In response to the specific absorption rate corresponding to the scan sequence exceeding a set threshold, the radio frequency pulse parameters of the scan sequence are adjusted.

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