MRI system, method for determining SAR value of MRI system, computer-readable storage medium

Abstract

The present invention relates to an MRI system, a method for determining the SAR value of an MRI system, and a computer-readable storage medium. The system includes a radio frequency (RF) transmitting coil, which is configured to receive RF power from an RF transmitting link and transmit the RF power required for imaging to a scanned object. The system further includes a reflection coefficient determination module, a resistance value determination module, and a SAR value determination module. The reflection coefficient determination module is configured to obtain the frequency response of a first input reflection coefficient when the RF transmitting coil is unloaded and the frequency response of a second input reflection coefficient when the scanned object is present. The resistance value determination module is configured to determine the resistance value of the RF transmitting coil based on the frequency response of the first input reflection coefficient and determine the parallel resistance value of the RF transmitting coil and the scanned object based on the frequency response of the second input reflection coefficient. The SAR value determination module is configured to calculate the SAR value of the scanned object based on the resistance value of the RF transmitting coil and the parallel resistance value.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging, and in particular, to a magnetic resonance imaging (MRI) system, a method for determining the SAR value in a magnetic resonance imaging system, and a computer-readable storage medium for executing the method. Background Art

[0002] In the process of imaging a scanned object using a magnetic resonance imaging system, a radio frequency excitation pulse is transmitted to the tissue to be imaged by a radio frequency transmitting coil. A large part of the power of the radio frequency excitation pulse is absorbed by the human body and converted into heat energy. If the tissue to be imaged absorbs too much radio frequency energy in a short time, local burns may occur and even greater safety problems may be caused.

[0003] To avoid such safety problems, during magnetic resonance scanning, it is usually necessary to monitor or evaluate the radio frequency energy absorption rate, also known as the SAR value (Specific Absorption Rate), to determine whether the heat absorbed by the human body exceeds the safe range.

[0004] In the prior art, a pick-up coil coupled to the radio frequency transmitting coil can be used to measure the coil loss in real time, and then the SAR value can be calculated using the coil loss. However, setting up this pick-up coil not only increases the hardware cost but also makes the system design more complex. Another way is to calculate the SAR value using a conservatively estimated coil loss value. However, too conservative an estimate will limit the selection of scanning parameters and is not conducive to obtaining an ideal image.

[0005] If a more accurate SAR value can be obtained, it can not only ensure the safety of the object but also be conducive to obtaining more reasonable scanning parameters. Especially for special patients such as infants, pregnant women, and those with implants, higher-quality images can be obtained on the premise of safe scanning. Summary of the Invention

[0006] One aspect of the present invention provides a magnetic resonance imaging system, including:

[0007] A radio frequency transmitting coil for receiving radio frequency power from a radio frequency transmitting link and transmitting the radio frequency power required for imaging to a scanned object;

[0008] A reflection coefficient determination module for obtaining the frequency response of the first input reflection coefficient when the radio frequency transmitting coil is unloaded and the frequency response of the second input reflection coefficient when there is a scanned object;

[0009] A resistance value determination module for determining the resistance value of the radio frequency transmitting coil based on the frequency response of the first input reflection coefficient and determining the parallel resistance value of the radio frequency transmitting coil and the scanned object based on the frequency response of the second input reflection coefficient; and,

[0010] A SAR value determination module is configured to calculate the SAR value of the scanned object based on the resistance value of the radio frequency transmitting coil and the parallel resistance value.

[0011] On the other hand, the reflection coefficient determination module is used to:

[0012] receiving a first forward signal and a first reverse signal detected when the radio frequency transmitting coil is unloaded;

[0013] The radio frequency transmitting coil detected by receiving has a second forward signal and a second reverse signal when scanning an object;

[0014] Calculating a frequency response of the first input reflection coefficient based on a frequency response of the first forward signal and a frequency response of the first reverse signal; and

[0015] The frequency response of the second input reflection coefficient is calculated based on the frequency response of the second forward signal and the frequency response of the second reverse signal.

[0016] On the other hand, the system further includes a signal receiving detection device provided at a transmission line port of the radio frequency transmission link, which is used to detect the first forward signal, the first reverse signal, the second forward signal and the second reverse signal.

[0017] On the other hand, the resistance determination module is configured to calculate the resistance of the RF transmitting coil based on a frequency response of the first input reflection coefficient and an intrinsic impedance of the RF transmitting link. The resistance determination module is further configured to calculate a parallel resistance between the RF transmitting coil and the scanned object based on a frequency response of the second input reflection coefficient and an intrinsic impedance of the RF transmitting link.

[0018] On the other hand, the frequency response of the first input reflection coefficient includes: a frequency response of the first input reflection coefficient at the resonant frequency of the RF transmitting coil when the RF transmitting coil is unloaded; and the frequency response of the second input reflection coefficient includes: a frequency response of the second input reflection coefficient at the resonant frequency of the RF transmitting coil when the RF transmitting coil has a scanning object.

[0019] The resistance determination module is further configured to: calculate the resistance of the RF transmitting coil based on a frequency response of the first input reflection coefficient at the resonant frequency and an intrinsic impedance of the RF transmitting link; and calculate the parallel resistance based on a frequency response of the second input reflection coefficient at the resonant frequency and an intrinsic impedance of the RF transmitting link.

[0020] On the other hand, the system further includes a memory for storing at least one of the frequency response of the first input reflection coefficient, the frequency response of the second input reflection coefficient, the resistance value of the RF transmitting coil, and the parallel resistance value.

[0021] On the other hand, the resistance value determination module calculates the resistance value of the RF transmitting coil based on the following formula:

[0022]

[0023] The resistance value determination module calculates the parallel resistance value of the RF transmitting coil and the scanned object based on the following formula:

[0024]

[0025] where, R ec is the resistance value of the RF transmitting coil, R el is the parallel resistance value of the RF transmitting coil and the scanned object, |S11| is the first input reflection coefficient when the operating frequency of the RF transmitting coil is ω a , |S11′| is the second input reflection coefficient when the operating frequency of the RF transmitting coil is ω b , Z0 is the characteristic impedance of the RF transmitting link, which is a known value, ω0 is the resonant frequency of the RF transmitting coil when no load is present, ω′0 is the resonant frequency of the RF transmitting coil when the scanned object is present, Q ec = R ec C ec ω0, Q el = R el C el ω0, where, C ec is the equivalent capacitance of the RF transmitting coil when no load is present, C el is the parallel equivalent capacitance of the RF transmitting coil and the scanned object when the scanned object is present.

[0026] On the other hand, the SAR value determination module is further configured to:

[0027] Receive the currently detected second forward signal and second reverse signal, and calculate the total RF power currently absorbed by the RF transmitting coil and the scanned object based on the currently detected second forward signal and second reverse signal;

[0028] Calculate the proportion of the RF power absorbed by the scanned object in the total RF power based on the ratio between the resistance value of the scanned object and the resistance value of the RF transmitting coil, where the resistance value of the scanned object is calculated based on the parallel resistance value and the resistance value of the RF transmitting coil; and,

[0029] The SAR value of the scanned object is calculated based on the total radio frequency power, the weight of the scanned object, and the proportion.

[0030] Another aspect of the present invention provides a method for determining a SAR value of a magnetic resonance imaging system, wherein the magnetic resonance imaging system includes a radio frequency transmitting coil, which is configured to receive radio frequency power from a radio frequency transmitting link and transmit radio frequency power required for imaging to a scanned object. The method includes:

[0031] Obtaining a frequency response of a first input reflection coefficient of the radio frequency transmitting coil when unloaded and a frequency response of a second input reflection coefficient when the radio frequency transmitting coil has a scanning object;

[0032] calculating the resistance value of the RF transmitting coil based on the frequency response of the first input reflection coefficient and determining the parallel resistance value of the RF transmitting coil and the scan object based on the frequency response of the second input reflection coefficient; and

[0033] The SAR value of the scanned object is calculated based on the resistance value of the radio frequency transmitting coil and the parallel resistance value.

[0034] On the other hand, the step of obtaining the first input reflection coefficient and the second input reflection coefficient includes:

[0035] receiving a first forward signal and a first reverse signal detected when the radio frequency transmitting coil is unloaded;

[0036] The radio frequency transmitting coil detected by receiving has a second forward signal and a second reverse signal when scanning an object;

[0037] Calculating a frequency response of the first input reflection coefficient based on a frequency response of the first forward signal and a frequency response of the first reverse signal; and

[0038] The frequency response of the second input reflection coefficient is calculated based on the frequency response of the second forward signal and the frequency response of the second reverse signal.

[0039] On the other hand, the method further includes: controlling a signal receiving detection device to detect the first forward signal, the first reverse signal, the second forward signal and the second reverse signal, wherein the signal receiving detection device is arranged at a transmission line port of the RF transmission link.

[0040] On the other hand, the first forward signal, the first reverse signal, the second forward signal, and the second reverse signal are detected during the process of adjusting the radio frequency of the magnetic resonance imaging system.

[0041] On the other hand, the first forward signal and the first reverse signal are detected when calibrating the magnetic resonance imaging system.

[0042] On the other hand, the second forward signal and the second reverse signal are detected during pre-scanning of the scanned object.

[0043] On the other hand, the resistance value of the RF transmitting coil is calculated based on the frequency response of the first input reflection coefficient and the characteristic impedance of the RF transmitting link; and,

[0044] The parallel resistance value is calculated based on the frequency response of the second input reflection coefficient and the characteristic impedance of the RF transmitting link.

[0045] On the other hand, the frequency response of the first input reflection coefficient includes: the frequency response of the first input reflection coefficient at the resonant frequency of the RF transmitting coil when the RF transmitting coil is unloaded; the frequency response of the second input reflection coefficient includes: the frequency response of the second input reflection coefficient at the resonant frequency of the RF transmitting coil when the RF transmitting coil has a scanned object; the method further includes: calculating the resistance value of the RF transmitting coil based on the frequency response of the first input reflection coefficient at the resonant frequency and the characteristic impedance of the RF transmitting link; and calculating the parallel resistance value based on the frequency response of the second input reflection coefficient at the resonant frequency, the resonant frequency, and the characteristic impedance of the RF transmitting link.

[0046] On the other hand, the resistance value of the RF transmitting coil is calculated based on the following formula:

[0047]

[0048] The parallel resistance value of the RF transmitting coil and the scanned object is calculated based on the following formula:

[0049]

[0050] On the other hand, the steps of calculating the SAR value include:

[0051] Receiving the currently detected second forward signal and the second reverse signal, and calculating the total RF power currently absorbed by the RF transmitting coil and the scanned object based on the current second forward signal and the second reverse signal; and,

[0052] Calculating the proportion of the RF power absorbed by the scanned object in the total RF power based on the ratio between the resistance value of the scanned object and the resistance value of the RF transmitting coil, wherein the resistance value of the scanned object is calculated based on the parallel resistance value and the resistance value of the RF transmitting coil; and,

[0053] Calculating the SAR value of the scanned object based on the total RF power, the weight of the scanned object, and the proportion.

[0054] On the other hand, the present invention also provides a magnetic resonance imaging system, comprising:

[0055] a radio frequency (RF) transmitting coil, which is configured to obtain RF power through an RF transmitting link and transmit the RF power required for imaging to a subject to be scanned; and a processor, which is configured to execute the method described in any of the above aspects.

[0056] On the other hand, the present invention also provides a computer-readable storage medium, which includes a stored computer program, wherein the method described in any of the above aspects is executed when the computer program is run.

[0057] It should be understood that the above brief description is provided to introduce some concepts further described in the detailed description in a simplified form. This does not mean identifying the key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages mentioned above or in any section of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] With reference to the accompanying drawings, the present invention will be better understood by reading the following description of non-limiting embodiments, wherein:

[0059] Figure 1 a schematic structural diagram of a magnetic resonance imaging system in some embodiments is shown;

[0060] Figure 2 a block diagram of a magnetic resonance imaging system according to an embodiment of the present invention is shown;

[0061] Figure 3 a schematic structural diagram of an RF transmitting link of an RF transmitting coil according to an embodiment of the present invention is shown;

[0062] Figure 4 a block diagram of a magnetic resonance imaging system according to another embodiment of the present invention is shown;

[0063] Figure 5 an RF equivalent circuit when the RF transmitting coil is unloaded is shown;

[0064] Figure 6 an RF equivalent circuit when the RF transmitting coil has a subject to be scanned is shown;

[0065] Figure 7 an exemplary diagram of a first frequency response curve of a first input reflection coefficient varying with the operating frequency of a magnetic resonance imaging system according to an embodiment of the present invention is shown;

[0066] Figure 8The flowchart of a method for determining the SAR value of a magnetic resonance imaging system according to some embodiments of the present invention is shown. Detailed implementation manners

[0067] The following will describe the detailed implementation manners of the present invention. It should be noted that in the specific description process of these implementation manners, for the sake of concise description, this specification cannot describe all features of the actual implementation manners in detail. It should be understood that in the actual implementation process of any implementation manner, just as in the process of any engineering project or design project, in order to achieve the specific goals of the developer and to meet system-related or business-related restrictions, various specific decisions are often made, and this will also change from one implementation manner to another. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present invention, some design, manufacturing, or production changes based on the technical content disclosed in this disclosure are just conventional technical means and should not be understood as the content of this disclosure being insufficient.

[0068] Unless otherwise defined, the technical terms or scientific terms used in the claims and the specification should have the ordinary meaning understood by those of ordinary skill in the technical field to which they belong. The "first", "second" and similar terms used in this specification and the claims do not indicate any order, quantity or importance, but are only used to distinguish different components. The terms such as "a" or "one" do not indicate a quantity limitation, but indicate that there is at least one. The terms such as "comprising" or "including" mean that the elements or items appearing before "comprising" or "including" cover the elements or items listed after "comprising" or "including" and their equivalent elements, and do not exclude other elements or items. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, nor are they limited to direct or indirect connections.

[0069] Figure 1 The structural schematic diagram of a magnetic resonance imaging (MRI) system is shown. The magnetic resonance imaging system 100 includes a scanner 110. The scanner 110 is used to perform magnetic resonance scanning on an object (such as a human body) 16 to generate image data of the region of interest of the object 16, and the region of interest can be a pre-determined imaging site or imaging tissue.

[0070] The magnetic resonance imaging system 100 may include a controller 130, which is coupled to the scanner 110 to control the scanner 110 to execute the above-mentioned magnetic resonance scanning process.

[0071] In one example, the scanner 110 may include a main magnet assembly 111, a table 112, a radio frequency (RF) generator 113, an RF power amplifier 119, an RF transmit coil 114, a surface coil 118, a gradient coil driver 115, a gradient coil assembly 116, and a data acquisition unit 117.

[0072] The main magnet assembly 111 generally includes a toroidal superconducting magnet defined within a housing, and the toroidal superconducting magnet is installed within a toroidal vacuum vessel. The toroidal superconducting magnet and its housing define a cylindrical space surrounding the object 16, such as Figure 1 the shown scanning cavity 120. The main magnet assembly 111 generates a constant magnetic field along the Z direction of the scanning cavity 120, i.e., the B0 field. Generally, a relatively uniform portion of the B0 field is formed in the central region of the main magnet.

[0073] The table 112 is used to carry the object 16 and travels along the Z direction in response to the control of the controller 130 to enter and exit the above-mentioned scanning cavity 120. For example, in one embodiment, the imaging volume of the object 16 can be positioned in the central region of the scanning cavity where the magnetic field intensity is relatively uniform, so as to facilitate scanning and imaging of the imaging volume of the object 16.

[0074] The above-mentioned Z direction is generally the direction extending from the head to the feet (or from the feet to the head) when the object 16 is positioned on the table 112. For example, the selected layer can be a slice at any position in the Z direction.

[0075] The magnetic resonance imaging system 100 uses the formed B0 field to emit a static magnetic field to the object 16 located in the scanning cavity, so that the precession of the protons in the resonance region within the object 16 is ordered, generating a longitudinal magnetization vector.

[0076] The RF generator 113 is used to generate RF pulses, such as RF excitation pulses, in response to the control signal of the controller 130. The RF power amplifier 119 is used to amplify the small-power signal generated by the RF generator 113 to generate a high-power RF signal capable of exciting human tissue. The high-power RF signal can be input to the RF transmit coil 114 via an RF transmission line, so that the RF transmit coil 114 emits an RF field B1 orthogonal to the B0 field to the object 16 to excite the atomic nuclei within the above-mentioned resonance region, generating a transverse magnetization vector.

[0077] The RF transmit coil 114 may include, for example, a body coil arranged along the inner periphery of the main magnet, or a local coil dedicated to local imaging.

[0078] When the RF excitation pulse ends, the proton groups dephase, the macroscopic transverse magnetization vector in the tissue gradually decays, and a free induction decay signal is generated during the process that the transverse magnetization vector of the object 16 gradually returns to zero, i.e., a magnetic resonance signal that can be collected.

[0079] The gradient coil driver 115 is configured to provide appropriate current / power for the gradient coil assembly 116 in response to a gradient pulse control signal or a shimming control signal issued by the controller 130.

[0080] On one hand, the gradient coil assembly 116 forms a varying magnetic field in the imaging space to provide three-dimensional position information for the above-mentioned magnetic resonance signals. On the other hand, it is used to generate a compensation magnetic field for the B0 field to shim the B0 field.

[0081] The gradient coil assembly 116 may include three gradient coils, which are used to generate magnetic field gradients respectively tilted to three mutually perpendicular spatial axes (such as the X-axis, Y-axis, and Z-axis). More specifically, the gradient coil assembly 116 applies a magnetic field gradient in the slice selection direction (such as the Z direction) to perform slice selection in the imaging region. Those skilled in the art understand that this slice is any one of a plurality of two-dimensional slices distributed along the Z direction in the three-dimensional imaging volume. When scanning this imaging region, the radio frequency transmit coil 114 responds to the above-mentioned I and Q radio frequency excitation signals, emits a radio frequency excitation pulse to this slice of the imaging region, and excites this slice. The gradient coil assembly 116 applies a magnetic field gradient in the phase encoding direction (such as the Y direction) to perform phase encoding on the magnetic resonance signals of the excited slice. The gradient coil assembly 116 applies a gradient field in the frequency encoding direction (such as the X direction) of the object 16 to perform frequency encoding on the magnetic resonance signals of the excited slice.

[0082] The above-mentioned radio frequency transmit coil 114 may be connected to a transmit / receive (T / R) switch (not shown). By controlling this transmit / receive switch, the body coil can be switched between the transmit and receive modes. In the receive mode, the radio frequency transmit coil can be used to receive magnetic resonance signals from the object 16.

[0083] The surface coil 118 is usually disposed close to the scanned part (region of interest) of the object 16 (for example, covering or laying on the body surface of the object 16). The surface coil 118 is also used to receive magnetic resonance signals from the object 16.

[0084] The data acquisition unit 117 is configured to acquire the above-mentioned magnetic resonance signals (such as received by the body coil or the surface coil) in response to a data acquisition control signal from the controller 130. In one embodiment, the data acquisition unit 117 may include, for example, a radio frequency preamplifier, a phase detector, and an analog / digital converter. The radio frequency preamplifier is used to amplify the magnetic resonance signals, the phase detector is used to perform phase detection on the amplified magnetic resonance signals, and the analog / digital converter is used to convert the phase-detected magnetic resonance signals from analog signals to digital signals.

[0085] The data acquisition unit 117 is further configured to respond to the data storage control signal of the controller 130 to store the digitized magnetic resonance signal (or echo) in the k-space. The k-space is the filling space of the original data of the magnetic resonance signal with spatial positioning encoding information. Specifically, the data acquisition unit 117 responds to the data storage control signal of the controller 130 and fills the digitized magnetic resonance signal into the k-space in a specific manner.

[0086] Those skilled in the art can understand that when imaging and scanning the object 16, the controller 130 can send sequence control signals to the above components of the scanner 110 (such as the radio frequency generator 113, the gradient coil driver 115, etc.) through a sequence generator (not shown in the figure), so that the scanner 110 executes a preset scanning sequence.

[0087] Moreover, during the process of performing the scan, the controller 130 can calculate the SAR value based on the feedback / detection signal (such as the coil loss of the radio frequency transmit coil 114), and set / regulate the scan parameters based on the calculated SAR value. The scan parameters can include, for example, the scan repetition time, the number of excitations, the intensity of the radio frequency transmit signal, the selection of the scan sequence, etc.

[0088] Those skilled in the art can understand that the above "scan sequence" refers to a combination of pulses with specific amplitude, width, direction, and timing applied during magnetic resonance imaging scans. These pulses usually can include, for example, radio frequency pulses and gradient pulses. The radio frequency pulses can include, for example, radio frequency transmit pulses for exciting protons in the human body to resonate, radio frequency refocusing pulses, etc. The gradient pulses can include, for example, slice selection gradient pulses, phase encoding gradient pulses, frequency encoding gradient pulses, etc. Usually, multiple scan sequences can be preset in the magnetic resonance system so that a sequence suitable for clinical detection requirements can be selected. The clinical detection requirements can include, for example, the imaging site, imaging function, imaging effect, etc.

[0089] Performing a magnetic resonance scan on the object 16 can include a positioning scan (three-plane scan) and a formal scan. One or more scan sequences can be executed during the positioning scan and the formal scan. Among them, during the positioning scan, at least one of the coronal positioning image, sagittal positioning image, and transverse positioning image of the object can be obtained, and the scan parameters of the formal scan, such as the scan range of the formal scan, can be determined based on the positioning image. Before executing one or more scan sequences of the positioning scan or the formal scan, a pre-scan can be automatically or manually performed. During the pre-scan process, frequency adjustment can be performed to determine the Larmor frequency of the proton resonance of this scan based on the magnetic resonance signal feedback at different frequencies, and radio frequency transmit intensity adjustment can be performed to determine the radio frequency transmit power of this scan based on the magnetic resonance signal feedback at different radio frequency transmit intensities.

[0090] In addition, frequency adjustment is also performed during system calibration of the magnetic resonance imaging system. This system calibration may be performed when the magnetic resonance imaging system leaves the factory or during its routine maintenance. Such calibration may be performed when the magnetic resonance imaging system is idle.

[0091] The magnetic resonance imaging system 100 may include an image reconstruction unit 140, which is configured to perform an inverse Fourier transform on the data stored in the k-space to reconstruct a three-dimensional image of the imaging volume of the object 16 or a series of two-dimensional slice images. Specifically, the image reconstruction unit 140 may communicate with the controller 130 to perform the above-mentioned image reconstruction.

[0092] The magnetic resonance imaging system 100 may include a processing unit 150, which may perform any required post-processing on any one of the above three-dimensional image or image sequence. Such post-processing may be an improvement or adaptive adjustment made to the image in terms of contrast, uniformity, sharpness, brightness, etc. Specifically, the processing unit 150 may communicate with the controller 130 to perform the image processing method of the embodiment of the present invention.

[0093] In one embodiment, the controller 130, the image reconstruction unit 140, and the processing unit 150 may respectively or jointly include a computer processor and a storage medium, on which a program for predetermined data processing to be executed by the computer processor is recorded. For example, programs for implementing scan processing, image reconstruction, image processing, etc. may be stored on the storage medium. For example, a program for implementing the method for determining the SAR value of the embodiment of the present invention may be stored. The above storage medium may include, for example, ROM, floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, or non-volatile memory card.

[0094] The magnetic resonance imaging system 100 may include a display unit 160, which may be used to display an operation interface and various data, images, or parameters generated during data acquisition and processing.

[0095] The magnetic resonance imaging system 100 includes an operation console 170, which may include user input devices such as a keyboard and a mouse, etc. The controller 130 may respond to control commands generated by the user based on the operation console 170 or operation panels / buttons provided on the main magnet housing, etc., to communicate with the scanner 110, the image reconstruction unit 140, the image processing unit 150, the display unit 160, etc.

[0096] Figure 2 A block diagram 200 of a magnetic resonance imaging system according to an embodiment of the present invention is shown, which may include Figure 1Some or all of the components of the system 100 shown, for example, the system 200 includes a radio frequency (RF) transmit coil 210, which is configured to receive RF power from an RF transmit link 220 and transmit the RF power required for imaging to a scan object.

[0097] Figure 3 An embodiment of the RF transmit link 220 is shown, as Figure 3 shown, the RF transmit link 220 may include a transmission line and transmission devices between an RF power source 221 and the RF transmit coil 210. The RF power source 221 may include an RF power amplifier. The transmission devices may include, for example, a beam splitter 223, which is configured to divide the RF signal output by the RF power source 221 into two orthogonal (90-degree phase difference) signals. One of the signals is transmitted to the birdcage RF transmit coil 210 via an I line 225, and the other signal is transmitted to the birdcage RF transmit coil 210 via a Q line 227.

[0098] As Figure 2 shown, the system 200 further includes a reflection coefficient determination module 230, a resistance value determination module 240, and a specific absorption rate (SAR) value determination module 250.

[0099] The reflection coefficient determination module 230 is configured to obtain the frequency response of the first input reflection coefficient of the RF transmit coil 210 when it is unloaded and the frequency response of the second input reflection coefficient when there is a scan object.

[0100] Those skilled in the art understand that when the RF transmit coil operates unloaded, there is no object to be imaged in the imaging region of the magnetic resonance imaging system. For example, there is no object to be imaged in the scan cavity formed by the main magnet. Therefore, the RF transmit pulses emitted by the RF transmit coil are not applied to the object to be imaged. When there is a scan object in the RF transmit coil, the object to be imaged may be positioned in the imaging region, thereby receiving the RF transmit pulses emitted by the RF transmit coil 210 and generating magnetic resonance signals that can be acquired in response to the RF transmit pulses.

[0101] The frequency response of the first input reflection coefficient of the RF transmit coil 210 and the frequency response of the second input reflection coefficient can be determined by the frequency response of the ratio (such as voltage ratio) or the square root of the ratio (such as power ratio) between the reverse signal and the forward signal transmitted to the RF transmit coil 210 when the RF transmit signal is transmitted to the port of the RF transmit coil 210 via the RF transmit link 220.

[0102] The resistance value determination module 240 is configured to calculate the resistance value of the RF transmit coil 210 based on the frequency response of the first input reflection coefficient, and calculate the parallel resistance value of the RF transmit coil 210 and its scanned object (such as the object to be imaged) based on the frequency response of the second input reflection coefficient. The SAR value determination module 250 is configured to calculate the SAR value of the scanned object based on the resistance value of the RF transmit coil and the parallel resistance value of the RF transmit coil and its scanned object.

[0103] Specifically, the reflection coefficient determination module 230 is configured to receive the frequency response of the first forward signal and the frequency response of the first reverse signal detected when the RF transmit coil 210 is unloaded, and calculate the frequency response of the first input reflection coefficient based on the detected frequency response of the first forward signal and the frequency response of the first reverse signal. The reflection coefficient determination module 230 is further configured to receive the frequency response of the second forward input signal and the frequency response of the second input reflection signal detected when the RF transmit coil 210 has a scanned object, and calculate the frequency response of the second input reflection coefficient based on the detected frequency response of the second forward input signal and the frequency response of the second input reflection signal.

[0104] Figure 4 FIG. 400 is a block diagram of a magnetic resonance imaging system according to another embodiment of the present invention, as Figure 4 shown, the system 400 further includes a signal receiving and detecting device 470, which detects the frequency response of the forward signal and the frequency response of the reverse signal (e.g., detects the forward signal and the reverse signal at different operating frequencies) at the port where the RF transmit link 220 transmits power to the RF transmit coil 210. Among them, the forward signal includes the first forward signal when unloaded and the second forward signal when having a scanned object, and the reverse signal includes the first reverse signal when unloaded and the second reverse signal when having a scanned object.

[0105] In one embodiment, the detecting device 470 may include a directional coupler and a power meter connected to the directional coupler. Specifically, when the RF power signal is output from a port including an I line and a Q line, the detecting device 470 may include a first directional coupler disposed on the I line and a power meter connected to the first directional coupler, and a second directional coupler disposed on the Q line and a power meter connected to the second directional coupler. The first directional coupler is configured to detect the forward signal and the reverse signal of the I line, and the second directional coupler is configured to detect the forward signal and the reverse signal of the Q line.

[0106] In one embodiment, the forward signal and the reverse signal detected by the detecting device 470 may be voltage signals, current signals, or power signals.

[0107] Further, when the forward signal and the reverse signal detected by the detection device 470 are voltage signals or current signals, the reflection coefficient determination module 230 is further configured to obtain the corresponding forward input power and input reflection power based on the forward signal and the reverse signal received from the detection device 470, respectively. For example, when the radio frequency transmitting coil 210 is unloaded, the first directional coupler detects the first forward signal and the first reverse signal of the I line, and the second directional coupler detects the first forward signal and the first reverse signal of the Q line. Then, the reflection coefficient determination module 230 obtains the first forward power P fwdI and the first reverse power P rflI of the I line based on the first forward signal and the first reverse signal of the I line, respectively, and obtains the first forward power P fwdQ and the first input reverse power P rflQ of the Q line based on the first forward signal and the first reverse signal of the Q line, respectively. When the radio frequency transmitting coil has a scanning object, the first directional coupler detects the second forward signal and the second reverse signal of the I line, and the second directional coupler detects the second forward signal and the second reverse signal of the Q line. Then, the reflection coefficient determination module 230 obtains the second forward power P' fwdl and the second reverse power P' rfll of the I line based on the second forward signal and the second reverse signal of the I line, respectively, and obtains the second forward power P' fwdQ and the second reverse power P' rflQ of the Q line based on the second forward signal and the second reverse signal of the Q line, respectively.

[0108] In one embodiment, the reflection coefficient determination module 230 is configured to obtain the sum P fwdI of the first forward power P fwdQ of the I line and the first forward power P f、I of the Q line, the sum P rflI of the first reverse power P rflQ of the I line and the first reverse power P r、I of the Q line, the sum P' fwdI of the second forward power P' fwdQ of the I line and the second forward power P' f of the Q line, and the sum P' rflI of the second reverse power P' fwdQ of the I line and the second reverse power P' r of the Q line.

[0109] Further, the reflection coefficient determination module 240 can obtain the first input reflection coefficient |S11| based on the following formula (1), and obtain the second input reflection coefficient |S11|' based on formula (2).

[0110]

[0111]

[0112] The frequency responses of the first input reflection coefficient |S11| and the second input reflection coefficient |S11|' can be expressed as the reflection coefficient values at multiple operating frequencies. For example, when the RF transmitting coil is unloaded, the first input reflection coefficient |S11| at multiple operating frequencies can be obtained, and when the RF transmitting coil has a scanning object, the second input reflection coefficient |S11|' at multiple operating frequencies can be obtained. The multiple operating frequencies can also respectively include the resonance frequency when unloaded and the resonance frequency when having a scanning object, that is, the frequency response of the first input reflection coefficient can include the frequency response of the first input reflection coefficient at the resonance frequency of the RF transmitting coil, and the frequency response of the second input reflection coefficient can include the frequency response of the second input reflection coefficient at the resonance frequency of the RF transmitting coil.

[0113] The resistance value determination module 240 can respectively determine the resistance value of the RF transmitting coil 210 and the above parallel resistance value according to the frequency responses of the first input reflection coefficient and the second input reflection coefficient determined above. The following will be combined with Figures 5 - 6 to be described in detail.

[0114] Figure 5 Fig. shows the RF equivalent circuit 500 when the RF transmitting coil 210 is unloaded. Among them, the circuit 500 includes the coil resistance R ec and the inductor L connected in parallel with the coil resistance ec and the capacitor C ec , the above coil resistance R ec , the inductor L ec and the capacitor C ec are connected in parallel to equivalently represent the unloaded RF transmitting coil 210, and its impedance is Z ec . The circuit 500 further includes the equivalent power supply U s and the RF transmitting link characteristic impedance Z0, which can be respectively used to equivalently represent the RF power source and its internal resistance.

[0115] Figure 6 Fig. shows the RF equivalent circuit 600 when the RF transmitting coil 210 has a scanning object. Among them, the circuit 600 includes the scanning object resistance R connected in parallel es and the coil resistance R ec , where the scanning object resistance R es is used to equivalently represent the scanning object of the RF transmitting coil 210, such as the object to be imaged, and R el is used to represent the parallel resistance after the parallel connection of the scanning object resistance R es and the coil resistance R ec . The circuit 600 further includes the total resistance R elThe inductor L connected in parallel el and capacitor C el , the above parallel resistor R el 、Inductance L el and capacitor C el The parallel circuit formed is used to equivalent the RF transmitting coil 210 and its scanning object, and its impedance is Z el The circuit 600 also includes an equivalent power supply U s And the intrinsic impedance Z0 of the RF transmission link.

[0116] refer to Figure 5 The first input reflection coefficient can be the ratio of the reverse signal to the forward signal when the RF transmitting coil is unloaded. Taking the voltage signal as an example, the equivalent power supply U s The voltage signal provided to the RF transmitting coil is V in , part of the RF power is absorbed by the unloaded RF transmitting coil, and the other part is reflected back to the transmission link. At the port where the RF transmitting link transmits power to the RF coil, it is manifested as the presence of the first forward signal, namely V f , and the first reverse signal, namely V r , then the first input reflection coefficient |S11| is

[0117] refer to Figure 6 The second input reflection coefficient can be the ratio of the input reflection signal to the forward input signal when the RF transmitting coil has a scanning object. Also, taking the voltage signal as an example, assuming that the equivalent power supply U s The voltage signal provided to the RF transmitting coil is V in , which is applied to the parallel equivalent circuit composed of the RF transmitting coil and the scanned object. Part of the RF power is absorbed by the parallel equivalent circuit, and the other part is reflected back to the RF transmitting link. At the port where the RF transmitting link transmits power to the RF coil, it is manifested as the presence of a second forward signal, namely V′ f , and the second reverse signal, namely V′ r , then the second input reflection coefficient |S11|′ is

[0118] Figure 5 The parameter values in satisfy the following formulas (3)-(8):

[0119]

[0120]

[0121]

[0122]

[0123] V in = V f + V r (7)

[0124]

[0125] where ω0 is the resonance frequency of the RF transmitting coil 210 when it is unloaded, and ω a is the operating frequency of the RF transmitting coil when it is unloaded.

[0126] Based on the above formulas (6)-(8), the following formula (9) can be obtained:

[0127]

[0128] Since then further according to formula (9), formula (10) is obtained:

[0129]

[0130] Further combining formulas (3)-(5), the following formula (11) can be obtained.

[0131]

[0132] When the RF transmitting coil 210 operates at the resonance frequency when it is unloaded, ω a is equal to ω0, and formula (11) can be transformed into formula (12).

[0133]

[0134] Based on a similar principle, the relationship formula (13) between the second input reflection coefficient |S11|′ and the parallel resistance R el can be obtained.

[0135]

[0136] where ω′0 is the resonance frequency of the RF transmitting coil when there is a scanning object.

[0137] When the RF transmitting coil 210 has a scanning object and operates at the resonance frequency, ω is equal to ω′0, and formula (13) can be transformed into formula (14).

[0138]

[0139] Since the first input reflection coefficient |S11| can be obtained by the reflection coefficient determination module 230 (for example, by formula (1)), and the intrinsic impedance Z0 of the RF transmission link is a known value, the resistance value of the RF transmission coil 210 can be calculated based on the first input reflection coefficient |S11| and the intrinsic impedance Z0 of the RF transmission link when the RF transmission coil operates at the resonant frequency ω0. For example, by solving formula (12), the coil resistance R ec Alternatively, the coil resistance R can be obtained by fitting formula (11) based on the frequency response of the first input reflection coefficient |S11| ec .

[0140] Furthermore, since the second input reflection coefficient |S11|′ can also be obtained via the reflection coefficient determination module 230 (e.g., via formula (2)), the parallel resistance value can be calculated based on the second input reflection coefficient |S11|′ when the RF transmitting coil operates at the resonant frequency ω′0 and the intrinsic impedance Z0 of the RF transmitting link, for example, by solving formula (14) to obtain the total resistance R el Alternatively, the parallel resistance R can be obtained by fitting formula (13) based on the frequency response of the second input reflection coefficient |S11|′ el .

[0141] Based on the principles described above, the reflection coefficient determination module 230 can obtain a first input reflection coefficient |S11| when the RF transmitting coil 210 is unloaded and a second input reflection coefficient |S11|′ when the RF transmitting coil 210 is loaded with a scanning object when the RF transmitting coil operates at a resonant frequency.

[0142] For example, when the RF transmitting coil operates at the resonant frequency ω0, the first forward signal and the first reverse signal can be detected by the detection device 470, and the reflection coefficient determination module 230 obtains the first forward power and the first reverse power based on the first forward signal and the first reverse signal, respectively, and calculates the first input reflection coefficient |S11| using the principle of formula (1).

[0143] Based on the frequency response of the first input reflection coefficient |S11|, the equivalent resistance R of the RF transmitting coil can be further obtained using the principle of formula (12): ec .

[0144] When the RF transmitting coil has a scanning object and operates exactly at the resonant frequency ω′0, the second forward input signal and the second input reflected signal can be detected by the detection device 470. The reflection coefficient determination module 230 obtains the second forward power and the second reverse power based on the second forward signal and the second reverse signal, respectively, and calculates the second input reflection coefficient |S11|′ using the principle of formula (2).

[0145] Based on the frequency response of the second input reflection coefficient |S11|′, the total equivalent resistance R of the RF transmit coil and the scanned object can be further obtained using formulas (14) and (15). el and the equivalent resistance R of the scanned object es .

[0146] Therefore, in another embodiment, the reflection coefficient determination module 230 is configured to obtain the frequency responses of the first input reflection coefficient and the second input reflection coefficient of the RF transmit coil 210. The frequency responses of the first input reflection coefficient are the input reflection coefficients at multiple operating frequencies (e.g., ω a = ω1, ω2, ω3...) of the RF transmit coil 210, and the frequency responses of the second input reflection coefficient are the input reflection coefficients at multiple operating frequencies (ω b = ω′1, ω′2, ω′3...) of the RF transmit coil 210 with the scanned object. The resistance value determination module 240 calculates the resistance value R of the RF transmit coil based on the multiple first input reflection coefficients and their corresponding operating frequencies (ω1, ω2, ω3...)) (the frequency responses of the first input reflection coefficient), the characteristic impedance Z0 of the RF transmit link, and the resonant frequency ω0 of the RF transmit coil 210 ec , and the resistance value determination module 240 also calculates the parallel resistance value R of the RF transmit coil and the scanned object based on the multiple second input reflection coefficients and their corresponding operating frequencies (ω′1, ω′2, ω′3...) (the frequency responses of the second input reflection coefficient), the characteristic impedance Z0 of the RF transmit link, and the center frequency ω′0 of the RF transmit coil 210 el .

[0147] For example, the resistance value determination module 240 can obtain the resistance value R of the RF transmit coil and the above parallel resistance value R by separately solving formulas (11) and (13). ec and the above parallel resistance value R el .

[0148] In one embodiment, the detection device 470 can be controlled to detect the first forward signal, the first reverse signal, the second forward signal, and the second reverse signal during the process of adjusting the RF frequency of the magnetic resonance imaging system. The adjustment of the RF frequency may itself exist in the workflow of the magnetic resonance imaging system. Therefore, there is no need to add an additional frequency change process to implement the detection of the forward input signal and the input reflection signal.

[0149] In addition, when the magnetic resonance imaging system has a scanning object, the second forward signal and the second reverse signal can be detected by the detection device during the parameter adjustment process before scanning the scanning object or during the pre-scanning of the scanning object. For example, the second forward signal and the second reverse signal can be detected by the detection device 470 during the pre-scanning of the scanning object. This pre-scanning can be performed before any scanning sequence is executed. For example, when any scanning sequence of the positioning scan or the formal scan is started, pre-scanning is first performed. During the pre-scanning stage, different radio frequency operating frequencies are tried to find the resonance (center) frequency. After determining the resonance frequency, imaging scanning can be performed based on this resonance frequency.

[0150] In one embodiment, the first input reflection coefficients at different operating frequencies can be pre-stored in the memory 480, and the memory 480 can be accessed by the resistance value determination module 240 to obtain the resistance value R of the radio frequency transmitting coil based on the frequency response of the first input reflection coefficient. ec 。

[0151] The second input reflection coefficients at different operating frequencies can also be pre-stored in the memory 480, so that the parallel resistance value R of the radio frequency transmitting coil and the scanning object can be obtained based on the frequency response of the second input reflection coefficient. el 。

[0152] The obtained resistance value R ec and the parallel resistance value R el can also be stored in the memory 480 to be accessed by the SAR value determination module 250.

[0153] In one embodiment, the reflection coefficient determination module 230 can also obtain a first frequency response curve of the first input reflection coefficient varying with the operating frequency of the radio frequency transmitting coil, and can further obtain a second frequency response curve of the second input reflection coefficient varying with the operating frequency of the radio frequency transmitting coil. Figure 7 Fig. shows an example of the first frequency response curve. In Figure 7 it, the horizontal axis represents the operating frequency of the magnetic resonance imaging system, and the vertical axis represents the input reflection coefficient. The first frequency response curve and the second frequency response curve can be obtained by the reflection coefficient determination module 230 through fitting operations based on the obtained multiple first input reflection coefficients and multiple second input reflection coefficients respectively. And the first frequency response curve and the second frequency response curve can also be pre-stored in the memory 480 so that the resistance value determination module 240 can obtain the resistance value of the radio frequency transmitting coil 210 and its parallel resistance value with the scanning object.

[0154] The SAR value of the scanned object can be further determined based on the determined resistance value of the RF transmitting coil 210 and the above-mentioned parallel resistance value. The following will further describe in combination with Figure 6 for details.

[0155] According to Figure 6 it can be known that the total resistance R el , the coil resistance R ec and the scanned object resistance R es satisfy the following relationship (15).

[0156]

[0157] Since the parallel resistance value R el and the resistance value R ec of the RF transmitting coil can be obtained according to the embodiments described above, therefore, the resistance value R es of the scanned object can be further obtained according to Formula 15.

[0158] When there is a scanned object, the total power (incident RF power) P' in actually transmitted to the RF transmitting coil currently is the current detected second forward power P' f minus the second reverse power P' r , that is:

[0159] P' in = P' f - P' r (16)

[0160] Among them,

[0161] A part of the actually transmitted total power P' in is absorbed by the RF transmitting coil 210, and the other part is absorbed by the scanned object. And the proportion η of the power absorbed by the scanned object in the total power P' in can be obtained through the following formula (17) or its deformation formula.

[0162]

[0163] Among them,

[0164] Since the SAR value SAR of the scanned object is the heat absorbed per unit weight of the scanned object per unit time, assuming the weight of the scanned object is M, the SAR value of the scanned object is the average power for this weight, and this average power can be expressed by the following formula (18):

[0165]

[0166] The current SAR value of the scanned object can be further calculated by the following formula (19) or its variant formula.

[0167]

[0168] Combining formula (18) and (19) can obtain the following formula (20).

[0169]

[0170] Therefore, the SAR value determination module 250 is further configured to receive the currently detected second forward signal and second reverse signal, calculate the total RF power currently absorbed by the RF transmitting coil and the scanned object based on the currently detected second forward signal and second reverse signal, and calculate the SAR value of the scanned object based on the total RF power, the weight of the scanned object, and the ratio between the resistance value of the scanned object and the resistance value of the RF transmitting coil. For example, the incident RF power P′ can be calculated based on formula (16) in , and the SAR value can be further calculated based on formula (19), (20) or their variant formulas.

[0171] Another embodiment of the magnetic resonance imaging system of the present invention may include:

[0172] An RF transmitting coil, which is configured to receive RF power from an RF transmitting link and transmit the RF power required for imaging to a scanned object;

[0173] A resistance value determination module, which is configured to obtain the resistance values of the RF transmitting coil and the scanned object; and,

[0174] An SAR value determination module, which is configured to determine the total RF power absorbed by the RF transmitting coil and the scanned object when the RF power is transmitted to the RF transmitting coil, and calculate the SAR value of the scanned object based on the ratio of the resistance values of the RF transmitting coil and the scanned object and the total RF power.

[0175] This embodiment is similar to the magnetic resonance imaging system of any of the above embodiments. One difference may be that the resistance values of the RF transmitting coil and the scanned object can be obtained by other means (for example, direct measurement or other evaluation means that can be more accurate) rather than based on the reflection coefficient. Or, the above resistance values are pre-stored in a memory (such as memory 480), and the resistance value determination module can access this memory to retrieve the resistance value for the SAR value determination module to calculate the SAR value. The pre-stored resistance values can be obtained by using the methods of any of the embodiments described in the present invention.

[0176] Figure 8FIG. 800 is a flowchart of a method for determining the SAR value of a magnetic resonance imaging system according to an embodiment of the present invention. The magnetic resonance imaging system may be the system described in any of the above embodiments. As Figure 8 shown, in step S810, the frequency response of the first input reflection coefficient |S11| of the radio frequency transmitting coil when it is unloaded and the frequency response of the second input reflection coefficient |S11|' when there is a scanned object are obtained. In step S820, the resistance value R of the radio frequency transmitting coil is calculated based on the frequency response of the first input reflection coefficient |S11| ec , and the parallel resistance value R of the radio frequency transmitting coil and the scanned object is calculated based on the frequency response of the second input reflection coefficient |S11|'. el In step S830, the SAR value of the scanned object is calculated based on the resistance value R of the radio frequency transmitting coil ec and the parallel resistance value R. el

[0177] Optionally, the following steps may further be included:

[0178] The signal receiving and detecting device is controlled to detect the first forward signal and the first reverse signal of the radio frequency transmitting coil when it is unloaded, and the second forward signal and the second reverse signal when the radio frequency transmitting coil has a scanned object. Wherein, the signal receiving and detecting device may include the above-mentioned directional coupler and the corresponding power meter or other power / voltage / current measuring devices connected to the coupler.

[0179] Specifically, the first forward signal, the first reverse signal, the second forward signal, and the second reverse signal may be detected during the process of adjusting the operating frequency of the radio frequency transmitting coil. For example, the above-mentioned forward signal and reverse signal may be detected and fed back by the detecting device during the process of adjusting the operating frequency of the radio frequency transmitting coil.

[0180] For example, the first forward signal and the first reverse signal may be detected during the system calibration of the magnetic resonance imaging system.

[0181] For another example, the second forward signal and the second reverse signal may be detected during the pre-scanning of the scanned object.

[0182] In step S810, the detected first forward signal and first reverse signal may be received, and the frequency response of the first input reflection coefficient |S11| is calculated based on the frequency response of the first forward signal and the frequency response of the first reverse signal; the detected second forward signal and second reverse signal may also be received, and the frequency response of the second input reflection coefficient |S11|' is calculated based on the frequency response of the second forward signal and the frequency response of the second reverse signal.

[0183] ​In one embodiment, the frequency responses of the first input reflection coefficient and the second input reflection coefficient are the input reflection coefficients when the RF transmit coil operates at the resonant frequency. For example, when the RF transmit coil operates at the resonant frequency, the forward signal and the reverse signal are detected, and the first input reflection coefficient and the second input reflection coefficient are calculated based on the detected signals. Then, in step S820, the resistance value of the RF transmit coil can be calculated based on the frequency response of the first input reflection coefficient at the resonant frequency and the characteristic impedance of the RF transmit link. Specifically, the resistance value of the RF transmit coil is calculated based on the first reflection coefficient, the characteristic impedance of the RF transmit link, and formula (12) or its variant formula.

[0184] In step S820, the parallel resistance value can also be calculated based on the frequency response of the second input reflection coefficient at the resonant frequency, the resonant frequency, and the characteristic impedance of the RF transmit link. Specifically, the parallel resistance value is calculated based on the second reflection coefficient, the characteristic impedance of the RF transmit link, and formula (14).

[0185] In another embodiment, the frequency responses of the first input reflection coefficient and the second input reflection coefficient respectively include multiple first input reflection coefficients and multiple second input reflection coefficients at multiple operating frequencies of the RF transmit coil. Then, in step S820, the resistance value of the RF transmit coil can be calculated based on the multiple first input reflection coefficients, their corresponding operating frequencies, the characteristic impedance of the RF transmit link, and the operating frequency of the RF transmit coil. For example, the resistance of the RF transmit coil is calculated based on formula (11). Correspondingly, in step S820, the parallel resistance value of the RF transmit coil and the scanning object can also be calculated based on the multiple second input reflection coefficients, their corresponding operating frequencies, the characteristic impedance of the RF transmit link, and the center frequency of the RF transmit coil. For example, the parallel resistance value is calculated based on formula (13).

[0186] Further, in step S810, the first frequency response curve of the first input reflection coefficient changing with the operating frequency of the RF transmit coil can be obtained, and the second frequency response curve of the second input reflection coefficient changing with the operating frequency of the RF transmit coil can be obtained. Then, in step S820, multiple first input reflection coefficient values on the first frequency response curve can be extracted, and multiple second input reflection coefficient values on the second frequency response curve can be extracted.

[0187] Step S830 may include the following steps:

[0188] Step 1: Receive the currently detected second forward signal and second reverse signal, and calculate the current incident radio frequency power based on the currently detected second forward signal and second reverse signal. This is considered to be the total radio frequency power currently absorbed by the radio frequency transmitting coil and the scanned object. For example, the current total radio frequency power can be calculated based on formula (16).

[0189] Step 2: Calculate the SAR value of the scanned object based on the total RF power, the weight of the scanned object, and the ratio between the resistance value of the scanned object and the resistance value of the RF transmitting coil. For example, the SAR value can be calculated based on formula (20) or its modified formula. Specifically, the second step may include:

[0190] The ratio of the radio frequency power absorbed by the scanned object to the total radio frequency power is calculated based on the ratio between the resistance value of the scanned object and the resistance value of the radio frequency transmitting coil (wherein the resistance value of the scanned object is calculated based on the parallel resistance value and the resistance value of the radio frequency transmitting coil), and the SAR value of the scanned object is calculated based on the total radio frequency power, the weight of the scanned object, and the ratio.

[0191] The reflection coefficient determination module 240 , the resistance determination module 240 , and the SAR value determination module 250 may include a memory 480 and a processor, respectively or collectively.

[0192] Therefore, the present invention may also provide another embodiment of a magnetic resonance imaging system, comprising a radio frequency (RF) transmit coil and a processor. The RF transmit coil is configured to obtain RF power through a RF transmit link and transmit the RF power required for imaging to a scanned object. The processor is configured to execute the method for determining the SAR value of a magnetic resonance imaging system according to any of the above embodiments. For example, the processor is configured to perform the following operations: obtain a frequency response of a first input reflection coefficient when the RF transmit coil is unloaded; obtain a frequency response of a second input reflection coefficient when the RF transmit coil is loaded with the scanned object; calculate a resistance value of the RF transmit coil based on the first input reflection coefficient; calculate a parallel resistance value of the RF transmit coil and the scanned object based on the second input reflection coefficient; and calculate the SAR value of the scanned object based on the resistance value of the RF transmit coil and the parallel resistance value.

[0193] In one embodiment, the reflection coefficient determination module 230, resistance determination module 240, and SAR value determination module 250 may each or jointly include a storage medium that stores a program for performing predetermined data processing to be executed by a computer processor. For example, the storage medium may store a program for implementing the method for determining a SAR value according to an embodiment of the present invention. The storage medium may include, for example, a ROM, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, or a non-volatile memory card.

[0194] Therefore, an embodiment of the present invention may further provide a computer-readable storage medium comprising a stored computer program, wherein when the computer program is executed, any embodiment of the above method for determining the SAR value of a magnetic resonance imaging system is performed.

[0195] Each embodiment of the present invention determines the coil resistance and the parallel resistance between the coil and the object being scanned based on the frequency response of the input reflection coefficient when the RF transmitting coil is unloaded and scanning the object. This determines the SAR value of the object being scanned based on these resistance and parallel resistance values. This eliminates the need for an additional pickup coil and avoids the design costs associated with reducing interference between the pickup coil and the RF transmitting coil. A comparison of SAR values obtained at different operating frequencies using embodiments of the present invention with SAR values obtained using a pickup coil at the corresponding operating frequencies reveals a maximum error of only 3.6%, demonstrating that the SAR values obtained using embodiments of the present invention are more accurate.

[0196] By obtaining a more accurate SAR value, the scanning parameters set based on the SAR value are more reasonable, and better image quality or clinical experience can be achieved under the premise of safe scanning. For example, if the accurate SAR value obtained is lower than the conservatively estimated SAR value, the scanning time can be appropriately reduced (for example, by setting a shorter repetition time TR) to meet higher imaging requirements. Of course, the scanning time setting is only one example of a parameter that can be adjusted or set. Other scanning parameters can also be adjusted based on the accurately calculated SAR value.

[0197] Moreover, by treating the RF transmitting coil as a whole, its input reflection coefficient can be quickly obtained, which is relatively simple to implement. For transmitting coils with multiple transmitting channels, there is no need to detect scattering parameters between each port to obtain the complete electrical parameters of the circuit. Instead, the port where the RF transmitting link of each channel transmits RF power to the RF transmitting coil only needs to independently measure the frequency response of the forward signal and the frequency response of the reverse signal of each channel, thereby reducing the complexity of the calculation and avoiding the delay problem caused by excessive signal detection.

[0198] The purpose of providing the above specific embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive, but the present invention is not limited to these specific embodiments. It should be understood by those skilled in the art that various modifications, equivalent substitutions, and changes may be made to the present invention, and as long as these changes do not violate the spirit of the present invention, they should all be within the scope of protection of the present invention.

Claims

1. A magnetic resonance imaging system, comprising: A radio frequency (RF) transmit coil, configured to receive RF power from an RF transmit link and transmit the RF power required for imaging to a subject; A reflection coefficient determination module, configured to obtain a frequency response of a first input reflection coefficient when the RF transmit coil is unloaded and a frequency response of a second input reflection coefficient when the subject is present; A resistance value determination module, configured to determine a resistance value of the RF transmit coil based on the frequency response of the first input reflection coefficient and determine a parallel resistance value of the RF transmit coil and the subject based on the frequency response of the second input reflection coefficient; And, A SAR value determination module, configured to calculate a SAR value of the subject based on the resistance value of the RF transmit coil and the parallel resistance value.

2. The system according to claim 1, wherein The reflection coefficient determination module is configured to: Receive a first forward signal and a first reverse signal detected when the RF transmit coil is unloaded; Receive a second forward signal and a second reverse signal detected when the subject is present in the RF transmit coil; Calculate the frequency response of the first input reflection coefficient based on the frequency response of the first forward signal and the frequency response of the first reverse signal; and, Calculate the frequency response of the second input reflection coefficient based on the frequency response of the second forward signal and the frequency response of the second reverse signal.

3. The system according to claim 2, further comprising a signal receiving and detecting device disposed at a transmission line port of the RF transmit link, configured to detect the first forward signal, the first reverse signal, the second forward signal, and the second reverse signal.

4. The system according to claim 1, wherein The resistance value determination module is configured to determine the resistance value of the RF transmit coil based on the frequency response of the first input reflection coefficient and the characteristic impedance of the RF transmit link, and the resistance value determination module is further configured to determine the parallel resistance value of the RF transmit coil and the subject based on the frequency response of the second input reflection coefficient and the characteristic impedance of the RF transmit link.

5. The system according to claim 1, wherein, The frequency response of the first input reflection coefficient includes: when the RF transmit coil is unloaded, the frequency response of the first input reflection coefficient at the resonant frequency of the RF transmit coil; The frequency response of the second input reflection coefficient includes: when the subject is present in the RF transmit coil, the frequency response of the second input reflection coefficient at the resonant frequency of the RF transmit coil; The resistance value determination module is further configured to: Determine the resistance value of the RF transmit coil based on the frequency response of the first input reflection coefficient at the resonant frequency and the characteristic impedance of the RF transmit link; and, Determine the parallel resistance value based on the frequency response of the second input reflection coefficient at the resonant frequency and the characteristic impedance of the RF transmit link.

6. The system according to claim 4 or 5, wherein It further comprises a memory, configured to store at least one of the frequency response of the first input reflection coefficient, the frequency response of the second input reflection coefficient, the resistance value of the RF transmit coil, and the parallel resistance value.

7. The system according to claim 4 or 5, wherein, The resistance value determination module calculates the resistance value of the RF transmit coil based on the following formula: The resistance determination module calculates the parallel resistance value of the RF transmitting coil and the scan object based on the following formula: wherein, R ec is the resistance value of the radio frequency transmitting coil, R el is the parallel resistance value of the radio frequency transmitting coil and the scanned object, |S11| is the first input reflection coefficient when the operating frequency of the radio frequency transmitting coil is ω a and |S11′| is the second input reflection coefficient when the operating frequency of the radio frequency transmitting coil is ω b , Z0 is the characteristic impedance of the radio frequency transmitting link, which is a known value, ω0 is the resonant frequency of the radio frequency transmitting coil under no-load conditions, ω′0 is the resonant frequency of the radio frequency transmitting coil with the scanned object, Q ec = R ec C ec ω0, Q el = R el C el ω0, wherein, C ec is the equivalent capacitance of the radio frequency transmitting coil under no-load conditions, and C el is the parallel equivalent capacitance of the radio frequency transmitting coil and the scanned object with the scanned object.

8. The system according to claim 2, wherein, The SAR value determination module is also used for: receiving a currently detected second forward signal and a second reverse signal, and calculating a total radio frequency power currently absorbed by the radio frequency transmitting coil and the scanned object based on the currently detected second forward signal and the second reverse signal; Calculating a proportion of the radio frequency power absorbed by the scanned object in the total radio frequency power based on a ratio between a resistance value of the scanned object and a resistance value of the radio frequency transmitting coil, wherein the resistance value of the scanned object is calculated based on the parallel resistance value and the resistance value of the radio frequency transmitting coil; as well as, The SAR value of the scanned object is calculated based on the total radio frequency power, the weight of the scanned object, and the proportion.

9. A method for determining a SAR value of a magnetic resonance imaging system, the magnetic resonance imaging system comprising a radio frequency transmitting coil configured to receive radio frequency power from a radio frequency transmitting link and transmit radio frequency power required for imaging to a scanned object, the method comprising: Obtaining a frequency response of a first input reflection coefficient of the radio frequency transmitting coil when unloaded and a frequency response of a second input reflection coefficient when the radio frequency transmitting coil has a scanning object; determining a resistance value of the radio frequency transmitting coil based on a frequency response of the first input reflection coefficient, and determining a parallel resistance value of the radio frequency transmitting coil and the scan object based on a frequency response of the second input reflection coefficient; as well as, The SAR value of the scanned object is calculated based on the resistance value of the radio frequency transmitting coil and the parallel resistance value.

10. The method according to claim 9, wherein, The step of obtaining the first input reflection coefficient and the second input reflection coefficient includes: receiving a first forward signal and a first reverse signal detected when the radio frequency transmitting coil is unloaded; The radio frequency transmitting coil detected by receiving has a second forward signal and a second reverse signal when scanning an object; Calculating a frequency response of the first input reflection coefficient based on a frequency response of the first forward signal and a frequency response of the first reverse signal; and The frequency response of the second input reflection coefficient is calculated based on the frequency response of the second forward signal and the frequency response of the second reverse signal.

11. The method according to claim 10, wherein, The control signal receiving detection device detects the first forward signal, the first reverse signal, the second forward signal and the second reverse signal, wherein the signal receiving detection device is arranged at the transmission line port of the radio frequency transmission link.

12. The method according to claim 11, wherein, The first forward signal, the first reverse signal, the second forward signal, and the second reverse signal are detected during the process of adjusting the operating frequency of the radio frequency transmitting coil.

13. The method according to claim 12, wherein, The first forward signal and the first reverse signal are detected when calibrating the magnetic resonance imaging system.

14. The method according to claim 12, wherein, The second forward signal and the second reverse signal are detected during a pre-scan of the scan object.

15. The method according to claim 9, wherein: Calculating the resistance value of the RF transmitting coil based on the frequency response of the first input reflection coefficient and the intrinsic impedance of the RF transmitting link; as well as, Calculate the shunt resistance value based on the frequency response of the second input reflection coefficient and the characteristic impedance of the RF transmission link.

16. The method according to claim 15, wherein the frequency response of the first input reflection coefficient includes: when the RF transmission coil is unloaded, the frequency response of the first input reflection coefficient at the resonant frequency of the RF transmission coil; the frequency response of the second input reflection coefficient includes: when the RF transmission coil has a scanned object, the frequency response of the second input reflection coefficient at the resonant frequency of the RF transmission coil; The method further includes: calculate the resistance value of the RF transmission coil based on the frequency response of the first input reflection coefficient at the resonant frequency and the characteristic impedance of the RF transmission link; and, calculate the shunt resistance value based on the frequency response of the second input reflection coefficient at the resonant frequency, the resonant frequency, and the characteristic impedance of the RF transmission link.

17. The method according to claim 15 or 16, wherein, Calculate the resistance value of the RF transmission coil based on the following formula: Calculate the shunt resistance value of the RF transmission coil and the scanned object based on the following formula: wherein, R ec is the resistance value of the radio frequency transmitting coil, R el is the parallel resistance value of the radio frequency transmitting coil and the scanned object, |S11| is the first input reflection coefficient when the operating frequency of the radio frequency transmitting coil is ω a and |S11′| is the second input reflection coefficient when the operating frequency of the radio frequency transmitting coil is ω b . Z0 is the characteristic impedance of the radio frequency transmitting link, which is a known value, ω0 is the resonant frequency of the radio frequency transmitting coil under no-load conditions, ω′0 is the resonant frequency of the radio frequency transmitting coil with the scanned object, Q ec = R ec C ec ω0, Q el = R el C el ω0, wherein, C ec is the equivalent capacitance of the radio frequency transmitting coil under no-load conditions, and C el is the parallel equivalent capacitance of the radio frequency transmitting coil and the scanned object with the scanned object.

18. The method according to claim 10, wherein, The steps of calculating the SAR value include: receive the currently detected second forward signal and second reverse signal, and calculate the total RF power currently absorbed by the RF transmission coil and the scanned object based on the current second forward signal and second reverse signal; calculate the proportion of the RF power absorbed by the scanned object in the total RF power based on the ratio between the resistance value of the scanned object and the resistance value of the RF transmission coil, wherein the resistance value of the scanned object is calculated based on the shunt resistance value and the resistance value of the RF transmission coil; and, calculate the SAR value of the scanned object based on the total RF power, the weight of the scanned object, and the proportion.

19. A magnetic resonance imaging system, comprising: an RF transmission coil for obtaining RF power through an RF transmission link and transmitting the RF power required for imaging to a scanned object; and a processor configured to execute the method according to any one of claims 9-18.

20. A computer-readable storage medium, the computer-readable storage medium comprising a stored computer program, wherein, Execute the method according to any one of claims 9-18 when the computer program is running.

Images