Magnetic resonance system and safety control method for magnetic resonance scanning

Abstract

The embodiment of the invention provides a magnetic resonance system and a safety control method of magnetic resonance scanning, the magnetic resonance scanning uses a coupling coil to excite a local volume of a scanning object, and the coupling coil is used for receiving a radio frequency excitation pulse from a body coil of the magnetic resonance system to generate a radio frequency field used for exciting the local volume. The safety control method comprises the steps that a whole-body SAR value monitored in real time is acquired, and the whole-body SAR value is acquired based on the body coil; determining a conversion coefficient in the magnetic resonance scanning process, and converting the current whole body SAR value into the current local SAR value of the local volume based on the conversion coefficient; and judging the safety state of the magnetic resonance scanning based on the current local SAR value.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the technical field of medical imaging, and in particular, to a magnetic resonance system and a safety control method for magnetic resonance scanning. BACKGROUND

[0002] Magnetic resonance systems have been widely applied in the field of medical diagnosis. A conventional magnetic resonance system usually has a main magnet, a radio frequency coil, a gradient coil, etc. The radio frequency coil transmits a radio frequency excitation signal to excite a scanning object to generate a magnetic resonance signal, and a medical image of the scanning object can be reconstructed based on the magnetic resonance signal.

[0003] At present, the radio frequency coil includes a transmit / receive coil or a receive coil. The transmit coil includes a body coil (or a whole body coil, Body Coil) for example, which is arranged along a scanning cavity to surround the scanning object. The body coil can transmit a radio frequency excitation pulse to generate a radio frequency excitation signal for exciting the whole body of the scanning object, and thus is suitable for whole body imaging. After the excitation is completed, the body coil can also be switched to a receive mode to receive the magnetic resonance signal from the scanning object.

[0004] A local coil can also be used as a receive coil. When a medical image of a local body part is needed, a corresponding local coil can be used to obtain better image quality. The local coil includes a head coil, a knee coil, a shoulder coil, a spine coil, a wrist coil, etc.

[0005] Some local coils can also be used as transmit coils. A switching module can be used to select the body coil or the local coil to be coupled to a radio frequency power amplifier to transmit a radio frequency excitation pulse and excite the whole body or a local volume of the object accordingly. When the local coil is selected as a transmit and / or receive coil, the body coil is decoupled and in a non-working state.

[0006] In the magnetic resonance scanning technology, the specific absorption rate (SAR value) is used to represent the radio frequency energy accumulated in the body of the scanning object. When the scanning object is scanned by magnetic resonance, the radio frequency power, the scanning time and other parameters are set to ensure that the SAR value is lower than a safety limit value. In general, different limit values are set for the whole body SAR value and the local SAR value of the local body part. When the local body part is imaged, estimating an accurate local SAR value is helpful to perform appropriate scanning (such as appropriate scanning time and radio frequency parameter setting) on the object under the premise of safety. SUMMARY

[0007] Embodiments of the present application provide a magnetic resonance imaging system, a radio frequency signal processing method thereof and a radio frequency coil.

[0008] According to one aspect of the embodiments of this application, a safety control method for magnetic resonance scanning is provided, wherein the magnetic resonance scanning uses a coupling coil to excite a local volume of the scanned object, the coupling coil being used to receive radio frequency excitation pulses from the body coil of the magnetic resonance system to generate a radio frequency field for exciting the local volume; the safety control method for magnetic resonance scanning includes: acquiring real-time monitored whole-body SAR values, wherein the whole-body SAR values ​​are acquired based on the body coil; determining a conversion coefficient during the magnetic resonance scanning process, and converting the current whole-body SAR values ​​into current local SAR values ​​of the local volume based on the conversion coefficients; and determining the safety status of the magnetic resonance scanning based on the current local SAR values.

[0009] According to another aspect of the embodiments of this application, a magnetic resonance system is provided, comprising: a body coil for transmitting radio frequency excitation pulses; a coupling coil for receiving the radio frequency excitation pulses from the body coil to generate a radio frequency field for exciting a local volume of a scanned object; and a processor for performing a safety control method for magnetic resonance scanning as described above.

[0010] Referring to the following description and accompanying drawings, specific implementation methods of the embodiments of this application are disclosed in detail, indicating how the principles of the embodiments of this application can be adopted. It should be understood that the implementation methods of this application are not limited in scope. Within the spirit and scope of the appended claims, the implementation methods of this application include many changes, modifications, and equivalents. Attached Figure Description

[0011] The accompanying drawings, which form part of the specification, are used to provide a further understanding of the embodiments of this application and illustrate the implementation methods of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other implementation methods based on these drawings without creative effort. In the drawings:

[0012] Figure 1 This is a schematic diagram of a magnetic resonance imaging system according to an embodiment of this application;

[0013] Figure 2 This is a schematic diagram of the body coil and coupling coil structure according to an embodiment of this application;

[0014] Figure 3 This is a flowchart of a safety control method for magnetic resonance scanning according to an embodiment of this application;

[0015] Figure 4 It is obtained according to one embodiment of this application. Figure 3 A flowchart of the method for determining the first ratio in the process;

[0016] Figure 5 This is a schematic diagram of the hardware setup for magnetic resonance scanning according to an embodiment of this application;

[0017] Figure 6 These are the distribution values ​​of the image signals obtained by magnetic resonance scanning according to embodiments of this application;

[0018] Figure 7 These are electric field distribution values ​​obtained through simulation;

[0019] Figure 8 This is a flowchart illustrating the determination of the safety status of a magnetic resonance scan based on the current local SAR value, according to one embodiment of this application.

[0020] Figure 9 This is a schematic diagram of the structure of a magnetic resonance system according to an embodiment of this application; and

[0021] Figure 10 This is a schematic diagram of the body coil and coupling coil structure according to another embodiment of this application. Detailed Implementation

[0022] Referring to the accompanying drawings, the foregoing and other features of the embodiments of this application will become apparent from the following description. Specific embodiments of this application are specifically disclosed in the description and drawings, illustrating partial implementations in which the principles of the embodiments of this application can be adopted. It should be understood that this application is not limited to the described embodiments; rather, the embodiments of this application include all modifications, variations, and equivalents falling within the scope of the appended claims.

[0023] In the embodiments of this application, the terms "first," "second," etc., are used to distinguish different elements by name, but do not indicate the spatial arrangement or chronological order of these elements, and these elements should not be limited by these terms. The term "and / or" includes any one or more of the terms listed in association and all combinations thereof. The terms "comprising," "including," "having," etc., refer to the presence of the stated features, elements, components, or assemblies, but do not exclude the presence or addition of one or more other features, elements, components, or assemblies.

[0024] In the embodiments of this application, the singular forms "a," "the," etc., including the plural forms, should be broadly understood as "a kind" or "a class" rather than limited to the meaning of "an." Furthermore, the term "the" should be understood to include both the singular and plural forms, unless the context explicitly indicates otherwise. Additionally, the term "according to" should be understood as "at least partially based on…," and the term "based on" should be understood as "at least partially based on…," unless the context explicitly indicates otherwise.

[0025] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments. The term "comprising / including" as used herein means the presence of a feature, integral, step, or component, but does not exclude the presence or addition of one or more other features, integrals, steps, or components.

[0026] For ease of understanding, Figure 1 A magnetic resonance system 100 according to some embodiments of the present invention is shown.

[0027] The operation of the magnetic resonance system 100 is controlled by an operator workstation 110, which includes an input device 114, a control panel 116, and a display 118. The input device 114 may be a joystick, keyboard, mouse, trackball, touch-activated screen, voice control, or any similar or equivalent input device. The control panel 116 may include a keyboard, touch-activated screen, voice control, buttons, sliders, or any similar or equivalent control device. The operator workstation 110 is coupled to and communicates with a computer system 120, which enables the operator to control the generation and viewing of images on the display 118.

[0028] Computer system 120 includes multiple components that communicate with each other via electrical and / or data connection module 122. Connection module 122 can be a direct wired connection, fiber optic connection, wireless communication link, etc. Computer system 120 may include a central processing unit (CPU) 124, memory 126, and image processor 128. In some embodiments, image processor 128 may be replaced by image processing functions implemented in CPU 124. Computer system 120 can be connected to archive media devices, permanent or backup storage, or a network. Computer system 120 can be coupled to and communicate with a separate system controller 130.

[0029] System controller 130 includes a set of components that communicate with each other via electrical and / or data connection modules 132. Connection module 132 can be a direct wired connection, fiber optic connection, wireless communication link, etc. System controller 130 may include CPU 131, pulse generator 133 communicating with operator workstation 110, transceiver (or RF transceiver) 135, memory 137, and array processor 139. In some embodiments, pulse generator 133 may be integrated into the resonant component 140 of magnetic resonance system 100.

[0030] The scanned object (or patient) 170 can be positioned within the cylindrical imaging volume 146 of the resonance assembly 140.

[0031] System controller 130 can receive commands from operator workstation 110 to instruct on the scanning sequence to be executed during a magnetic resonance scan of the scanned object 170. The aforementioned "scanning sequence" refers to a combination of pulses with specific intensities, shapes, and timings applied during a magnetic resonance scan; these pulses typically include, for example, radio frequency pulses and gradient pulses. Multiple scanning sequences can be pre-stored in computer system 120 to enable the operator workstation to instruct on sequences adapted to clinical testing needs, which may include, for example, imaging site, imaging function, imaging effect, scan safety, etc. The pulse generator 133 of system controller 130, based on the instructed sequence, sends instructions describing the timing, intensity, and shape of the radio frequency pulses and gradient pulses in the sequence to operate system components executing the sequence.

[0032] Radio frequency (RF) pulses in the scan sequence transmitted by pulse generator 133 can be generated via transceiver 135, and these RF pulses are amplified by RF power amplifier 162. The amplified RF pulses are provided to an RF transmitting coil, such as body coil 148, via transmit / receive switch 164, which then provides a transverse magnetic field B1. As a non-limiting example, the transmitting portion of transceiver 135, RF power amplifier 162, T / R switch 164, etc., constitute at least a portion of the RF transmitting link. This transverse magnetic field B1 is substantially perpendicular to B0 throughout the cylindrical imaging volume 146, and is used to excite stimulated nuclei within the scanned object 170 to generate a magnetic resonance signal.

[0033] System controller 130 also provides gradient waveforms to gradient driver system 150, which includes G x (x direction), G y (y-direction) and G z (z-direction) amplifiers, etc. Each G x G y and G z The amplifiers excite the corresponding gradient coils in the gradient coil assembly 142 to generate a magnetic field gradient for spatial encoding of the magnetic resonance signal during magnetic resonance scanning. The gradient coil assembly 142 is disposed within the resonance assembly 140. The x-direction can also be referred to as the frequency encoding direction or the kx-direction in K-space, and the y-direction can be referred to as the phase encoding direction or the ky-direction in K-space. x It can be used for frequency coding or signal readout, and is often referred to as the frequency coding gradient or readout gradient. G y It can be used for phase coding, and is often referred to as the phase coding gradient. G z It can be used for slice (layer) location selection to obtain K-space data. It should be noted that the layer selection direction, phase encoding direction, and frequency encoding direction can be modified according to actual needs.

[0034] The resonant assembly 140 also includes a superconducting magnet with a superconducting coil 144 that provides a static, uniform longitudinal magnetic field B0 throughout the cylindrical imaging volume 146 during operation.

[0035] The resonant assembly 140 also includes a body coil 148, which can be used to transmit radio frequency pulses and provides a transverse magnetic field B1 in transmit mode operation, which is substantially perpendicular to B0 throughout the cylindrical imaging volume 146. The body coil 148 can also be used to receive magnetic resonance signals from the scanned object. The body coil 148 can be configured by a transmit / receive switch (T / R switch) 164 to operate in either transmit or receive mode. Specifically, the T / R switch 164 can be controlled by a signal from the system controller 130 to electrically connect the radio frequency power amplifier 162 to the RF body coil 148 during transmit mode and to connect the preamplifier 166 to the RF body coil 148 during receive mode.

[0036] A coupling coil (or surface coil) 149 may also be provided, and a body coil, coupling coil, or surface coil may be used to receive the magnetic resonance signal generated by the scanned object, which can be sent back to the preamplifier 166 via a T / R switch 164.

[0037] In some embodiments, the magnetic resonance signal sensed and received by any of the aforementioned coils and amplified by preamplifier 166 is stored as a raw k-space data array in memory 137 for post-processing. A reconstructed magnetic resonance image can be obtained by transforming / processing this stored raw k-space data.

[0038] In some implementations, the magnetic resonance signal sensed and received by the coil and amplified by the preamplifier 166 is demodulated, filtered, and digitized in the receiving section of the transceiver 135 and transmitted to the memory 137 in the system controller 130. For each image to be reconstructed, the data is rearranged into separate k-space data arrays, and each of these separate k-space data arrays is input to an array processor 139, which is operated to perform a Fourier transform on the data into an array of image data.

[0039] The array processor 139 uses a transformation method, most commonly Fourier transform, to reconstruct images from the received magnetic resonance signals. These images are transmitted to the computer system 120 and stored in the memory 126. In response to commands received from the operator workstation 110, the image data may be stored in long-term memory, or it may be further processed by the image processor 128 and transmitted to the operator workstation 110 for display on the monitor 118.

[0040] In various implementations, components of computer system 120 and system controller 130 may be implemented on the same computer system or multiple computer systems. System controller 130 and image processor 128 may each 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, the storage medium may store programs for performing scan processing (e.g., scan procedure, imaging sequence), image reconstruction, image processing, etc. For instance, it may store programs for implementing the safety control method for magnetic resonance scanning according to embodiments of the present invention. The aforementioned storage medium may include, for example, ROM, floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, or non-volatile memory card.

[0041] It should be understood that Figure 1 The magnetic resonance system 100 shown is for illustrative purposes. Suitable magnetic resonance systems may include more, fewer, and / or different components.

[0042] The inventors discovered that coupling coils used to transmit radio frequency excitation signals and / or receive magnetic resonance signals require cables for power supply and connection to decoupling circuits. As the number of channels increases, the complexity of the cable interfaces and cables also increases, thereby increasing costs.

[0043] For self-transmitting and self-receiving coupling coils, in addition to the receiving cables, receiving channels, and decoupling circuits described above, the coupling coil also needs to be electrically connected to the RF transmitting link (e.g., including an RF power amplifier) ​​to receive RF excitation pulses from the RF transmitting link, which also increases the wiring complexity. Furthermore, the electrical structure of such coupling coils is usually mounted on rigid materials.

[0044] Therefore, a coupling coil for a magnetic resonance imaging system is proposed. This coupling coil is used to engage with a region of an object (e.g., object 170) to be scanned and is coupled to the magnetic resonance system in a wireless manner. For example, the coupling coil can be used to wrap around / surround / cover / approach the region of the object to be scanned, including local body parts such as the shoulder, head, knee, limbs, ankle, and wrist. This coupling coil is used to connect with the body coil of the magnetic resonance system (e.g., ...). Figure 1 The coupling coil is coupled to the body coil 148 to receive radio frequency pulses emitted from the body coil, thereby generating a radio frequency field that excites the scanned object 170. The coupling coil also sends the magnetic resonance signal received from the object 170 to the body coil, thus realizing magnetic resonance scanning of the part of the object 170 to be scanned.

[0045] Figure 2 A schematic diagram of the structure of the body coil and the coupling coil is shown, as follows: Figure 2As shown, an RF shield 23 is introduced between the body coil 21 and the gradient coil (not shown). When the body coil 21 has a birdcage-like structure (orthogonal coil), the coupling coil 22 also has a roughly birdcage-like structure, and the electrical structure therein constitutes an orthogonal coil. During scanning, the coupling coil 22 is located inside the body coil 21 and positioned at the area of ​​the object to be imaged. The volume of the coupling coil 22 is smaller than the volume of the body coil 21. For example, the maximum length L1 and maximum diameter D1 of the coupling coil are both smaller than the maximum length L2 and maximum diameter D2 of the body coil 21. However, the values ​​of the length and diameter of the coupling coil 22 are related to the area to be imaged, and this embodiment is not intended to limit them.

[0046] In some embodiments of this application, the coupling coil 22 and the body coil 21 have the same electrical or electromagnetic structure. The above example uses the example that both the body coil 21 and the coupling coil 22 have a birdcage-like structure. However, this embodiment of the application is not limited to this. When the body coil 21 has other electrical structures, the coupling coil 200 may also include a similar electrical structure.

[0047] Utilizing electromagnetic principles, during scanning, the coupling coil 22 and the body coil are brought close together, resulting in strong electromagnetic coupling. Therefore, when the body coil 21 emits a radio frequency (RF) pulse, a current is induced in the coupling coil 22. This induced magnetic field transmits the RF pulse from the body coil 21 to the coupling coil 22, generating a uniform magnetic field B1 that excites the scanned area of ​​the object to resonate, producing a transverse magnetization vector. After the RF pulse emission is complete (and the magnetic field B1 is removed), a magnetic resonance signal is generated under the action of a gradient sequence of pulses, which is then sensed and received by the coupling coil 22. Similarly, when the coupling coil receives the magnetic resonance signal, a current is induced in the body coil 21, which uses the induced magnetic field to transmit the signal from the coupling coil 22 to the body coil 21. This signal is then transmitted via a transmission cable connected to the body coil 21 to the system's receiver module, where it is processed and a magnetic resonance image is reconstructed.

[0048] In some embodiments, the coupling coil 22 is flexible. In the closed state, the radio frequency coil is birdcage-shaped, and in the open state, the coupling coil 22 can be unfolded into a sheet-like structure. When scanning an object is required, the coupling coil can be unfolded and bent to surround the area to be scanned on the object, and then the coupling coil is closed so that it follows the object into the center of the scanning cavity. During magnetic resonance scanning, radio frequency pulses emitted from the body coil 21 are received via the coupling coil 22 to generate a radio frequency field that excites the area to be scanned on the object; and the magnetic resonance signal received from the object is transmitted to the body coil via the coupling coil, wherein the coupling coil and the body coil are electromagnetically coupled.

[0049] In some embodiments, the body coil 21 and the coupling coil 22 transmit and receive radio frequency signals wirelessly via electromagnetic coupling (mutual inductance). Unlike traditional coupling coils, which require their own cables, receiving channels, and / or transmitting chains for magnetic resonance signal transmission, the coupling coil 22 does not need to be electrically connected to other structures in the magnetic resonance imaging system. In other words, the coupling coil 22 is independent, requiring no cable interface or connection to the detection bed via cable. It can achieve self-transmission and self-reception of radio frequency signals, eliminating the need for DC power to switch transmission / reception modes, decoupling circuits found in traditional coil array structures, and additional receiving and / or transmitting chain modules (e.g., no corresponding receiving and / or transmitting chain modules for traditional coil arrays). Magnetic resonance scanning of localized areas of the object can be achieved using only the receiving and transmitting links of the system connected by the body coil 21. In other words, radio frequency signals are received and transmitted through electromagnetic coupling between the body coil 21 and the coupling coil 22 without cables or cable interfaces. This simplifies the wiring of the magnetic resonance system, simplifies the circuit structure, improves reliability, reduces the failure rate, reduces costs, and makes it easy to handle.

[0050] When the object being scanned is located inside the scanning cavity, the body coil 21 is far from the part to be imaged and cannot generate a strong magnetic field near the center of the part to be imaged. By using a small-volume coupling coil 22 that is closer to the part to be imaged and is similar in size to the part to be imaged to transmit and receive radio frequency signals, the same B1 field can be generated by the object with less energy, thereby further improving the signal-to-noise ratio.

[0051] The radio frequency coil uses the same electromagnetic structure as the body coil, such as a birdcage coil structure, which enables the generation of a more uniform magnetic field and further improves the signal-to-noise ratio.

[0052] Despite these advantages, similar to traditional RF transmitting coils, a portion of the RF power emitted by the coupled coil, which is wirelessly coupled to the body coil, is still absorbed by the scanned object. The accumulation of absorbed RF energy can cause localized burns in the imaged area. Therefore, such RF transmitting coils also require real-time monitoring of the contrast absorptivity (SAR value). Those skilled in the art will understand that international standards specify safety limits for whole-body SAR and local SAR. Whole-body SAR is the average SAR of the entire human body, which can be accurately obtained through electrical signal monitoring during MRI scans. Local SAR is the SAR value of local tissues, including, for example, head SAR and limb SAR, which are typically difficult to measure directly during MRI scans.

[0053] In particular, when the coupling coil used for radio frequency excitation is not electrically connected to the radio frequency transmission link, but is wirelessly coupled to the body coil to concentrate the radio frequency energy emitted by the body coil in a local area, the SAR value monitored by the electrical signal (based on the body coil) differs greatly from the actual SAR experienced by that area. Therefore, the monitored SAR value cannot be used as the true SAR value to determine whether the current scan is safe.

[0054] To enable safe magnetic resonance scanning of a target object, embodiments of this application provide a safe control method for magnetic resonance scanning. This magnetic resonance scan uses a coupling coil to excite a local volume of the target object. The coupling coil receives radio frequency excitation pulses from the body coil of the magnetic resonance system to generate a radio frequency field for exciting the local volume. The specific structures of the coupling coil and the body coil can be as follows: Figure 2 As shown, it can also have other deformable structures.

[0055] like Figure 3 The diagram shows a flowchart of one embodiment of the safety control method for magnetic resonance imaging (MRI) scanning. In step 31, the real-time monitored whole-body SAR value is acquired. This whole-body SAR value is obtained based on the body coil. For example, it can be calculated by real-time monitoring of the radio frequency output signal of the radio frequency power amplifier connected to the body coil, and by combining parameters such as the frequency and flip angle of the radio frequency signal with the size of the body coil and the weight of the scanned object. In step 32, a conversion factor (e.g., defined as R) is determined during the MRI scan, and the current whole-body SAR value is converted into the current local SAR value for the local volume based on the conversion factor R. In step 33, the safety status of the MRI scan is determined based on the current local SAR value.

[0056] In embodiments of the present invention, by determining the conversion coefficient R during magnetic resonance scanning, even if the coupling coil is not electrically coupled to the radio frequency link, a local SAR value close to the actual value can be obtained in real time. Based on the local SAR value, the safety status of magnetic resonance scanning is judged, avoiding the situation where magnetic resonance scanning cannot continue due to the limitation of the whole-body SAR value when the actual local SAR value does not reach the safety limit, or avoiding the safety problem of local volume caused by continuing magnetic resonance scanning only in response to the whole-body SAR not reaching the limit, which would result in the local SAR value exceeding the limit.

[0057] In embodiments of the present invention, the conversion coefficient R can be the ratio between the whole-body SAR value and the local volume SAR value, wherein the current local volume SAR value is the product of the current whole-body SAR value and the conversion coefficient.

[0058] In embodiments of the present invention, the conversion coefficient is obtained based on the electric field distribution and the mass density distribution of the scanned object during the magnetic resonance scan. The electric field distribution includes the electric field distribution inside and outside the coupling coil, and the mass density distribution includes the mass density inside the body coil and the mass density inside the coupling coil.

[0059] Specifically, the conversion coefficient can be obtained based on a first ratio R1 and a second ratio R2, wherein the first ratio R1 is the ratio between the electric field inside the volume of the coupling coil and the electric field outside the volume of the coupling coil, and the second ratio is the ratio between the mass density inside the volume of the body coil and the mass density inside the volume of the coupling coil.

[0060] In embodiments of this application, the electric field distribution can be obtained using the current magnetic resonance scan. Specifically, the ratio of the electric field distribution, such as the first ratio mentioned above, can be obtained from image information obtained during the magnetic resonance scan. More specifically, this first ratio can be obtained from image information obtained during the pre-scanning phase of the magnetic resonance scan.

[0061] Those skilled in the art will understand that in the magnetic resonance imaging (MRI) scan process, a pre-scan (or calibration scan) is required before the formal scanning and imaging of the region of interest. This pre-scan calibrates the system parameters, determining the scanning parameters to be used in the formal scan. These parameters may include, for example, radio frequency transmit gain (TG), radio frequency signal center frequency, and gradient shim value. Because the physiological characteristics of the scanned object vary from person to person, the scanning equipment may be affected by different factors, and the scanned object will also cause changes in the magnetic field. Therefore, performing a pre-scan allows for the acquisition of calibrated parameters, which, when applied to the formal scan, ensure sufficiently good image quality. For example, according to a set scanning protocol, the flip angle of the radio frequency excitation pulse should be 90 degrees. The pre-scan can determine parameters such as radio frequency transmit gain and frequency, ensuring that when these parameters are applied to the formal scan, the actual flip angle of the macroscopic magnetization vector of the tissue by the actual radio frequency field can reach 90 degrees.

[0062] Pre-scanning typically uses low-energy radio frequency pulses and the pre-scanning time is short. In the embodiments of this application, the first ratio is obtained based on the image signal acquired in the pre-scanning stage, without adding an extra scanning process (or scanning stage) to the magnetic resonance scan, and without additional energy consumption and time consumption.

[0063] Will be combined below Figure 4 to Figure 7 The method for obtaining the first ratio is explained in detail.

[0064] like Figure 4The diagram illustrates a flowchart of a method for obtaining the first ratio in an embodiment of this application. In step 41, during the pre-scanning phase of a magnetic resonance imaging (MRI) scan, a first image signal and a second image signal are acquired. The first image signal is an image signal within the volume of the coupling coil, and the second image signal is an image signal within the volume of the body coil. In step 43, the ratio between the first image signal and the second image signal is obtained as the first ratio.

[0065] Figure 5 This is a schematic diagram of the hardware setup for magnetic resonance scanning according to an embodiment of this application, showing a body coil 51, a coupling coil 52, a phantom 53 located within the coupling coil 52, and a phantom 54 located outside the coupling coil 52. The phantoms 53 and 54 may be the same or different phantoms. Figure 5 The phantom used in the experiment is shown as the tissue to be imaged. During actual scanning, the phantom 53 located within the coupling coil 52 can be replaced with the area to be imaged from the scanned object, such as the knee, while the phantom 54 located outside the coupling coil 52 can be replaced with other areas of the scanned object. In practical applications, this other area is selected outside the coupling coil 52, but preferably close to it, for example, tissue located within the FOV (Field of View) is selected as this other area. For example, this other area could be the thigh or calf near the knee, or it could be the other knee of the scanned object.

[0066] In step 41 above, when the RF power amplifier outputs the same RF power, the presence of the coupling coil causes different flip angles inside and outside the coupling coil. For example, the image signal I1 obtained by imaging the phantom 53 inside the coupling coil is used as the first image signal, which has a first flip angle (e.g., α1). The image signal I2 obtained by imaging the phantom 54 outside the coupling coil is used as the second image signal, which has a second flip angle (e.g., α2), where the first flip angle is greater than the second flip angle. In step 43, the ratio of I1 to I2 is obtained as the first ratio.

[0067] Figure 6 The distribution values ​​of the aforementioned image signals I1 and I2 obtained via magnetic resonance scanning are shown, where the horizontal axis represents the position coordinates and the vertical axis represents the logarithmic representation of the image signal values, in dB. Figure 6 The signal value within the ellipse 61 corresponds to image signal I1, which is normalized to 0. The signal value within the ellipse 62 corresponds to image signal I2, which is distributed around -22dB. Therefore, the ratio of I1 to I2 is approximately 100.

[0068] Figure 7The electric field distribution values ​​obtained through simulation are shown, where the electric field value inside elliptical loop 71 corresponds to the electric field value inside the coupling coil, and is normalized to 0. The electric field value inside elliptical loop 72 corresponds to the electric field value outside the coupling coil, which is also distributed at around -22dB. It can be seen that the first ratio obtained through the embodiments of this application is consistent with the actual electric field ratio.

[0069] In the embodiments of this application, during the pre-scanning stage of magnetic resonance scanning, the radio frequency excitation pulse has a small flip angle, for example, less than 30 degrees, preferably less than 20 degrees. The inventors have discovered that the following relationship is satisfied at a small flip angle:

[0070]

[0071] Wherein, B1.1 is the electromagnetic field inside the coupling coil and B1.2 is the electromagnetic field outside the coupling coil. Therefore, the first ratio R1 of the image signals I1 and I2 obtained in the pre-scanning stage of magnetic resonance scanning is closer to the actual electric field ratio, so that the accurate conversion coefficient can be obtained in the end, and a more realistic local SAR value can be obtained.

[0072] In the embodiments of this application, the aforementioned pre-scan can employ a gradient echo sequence to perform imaging scanning on the scanned object to obtain the first image signal and the second image signal. Using a gradient echo sequence can yield a first ratio that closely approximates the actual value.

[0073] In the embodiments of this application, the mass density within the volume of the body coil can be determined based on the volume of the body coil and the mass of the scanned object within that volume. In one example, when the entire body of the scanned object is located within the body coil, the quotient between the weight of the scanned object and the volume of the body coil can be calculated as the mass density.

[0074] Accordingly, the mass density within the volume of the coupling coil can be determined based on the volume of the coupling coil and the mass of the scanned object within that volume. In one example, the mass of the body part enclosed by the coupling coil can be determined by the proportion of its mass to the total mass, similar to a predetermined human body mass model. For example, in an example human body mass model, the mass of the body part can be determined based on the correspondence between one or more physiological characteristics such as height, weight, gender, and age and the proportion of different body parts to the total mass.

[0075] The volume of the body coil and the coupling coil can be determined based on the radius and length of the coil.

[0076] The table below provides an example of obtaining the aforementioned second ratio. As shown, the volumes of the body coil and coupling coil can be calculated based on the cylinder volume formula, using the coil radius and length respectively. The masses of the imaging tissue within these volumes are 40 kg and 10 kg, respectively. Dividing the corresponding mass values ​​by the corresponding coil volumes yields the corresponding mass densities. The ratio between the mass density within the body coil and the mass density within the coupling coil is taken as the second ratio R2, for example, 1 / 9.75.

[0077] Parameter / Unit Body coil Coupling coil First ratio Coil radius / cm 300 100 / Coil length / cm 650 300 / Mass in volume / kg 40 10 / Volume / mm^3 367380000 9420000 / Mass density / kg / mm^3 1.08879E-07 1.0616E-06 1 / 9.75

[0078] The conversion coefficient R can be the product of the first ratio R1 and the second ratio R2. For example, R = 100 * (1 / 9.75) ≈ 10.

[0079] Figure 8 A flowchart illustrating the determination of the safety status of a magnetic resonance imaging (MRI) scan based on the current local SAR value, according to an embodiment of this application, is shown. In step 81, it is determined whether the obtained conversion coefficient R is greater than a preset upper limit ratio. If so, step 82 is executed, i.e., determining whether the current local SAR value has reached its upper limit value. For example, if the preset ratio is 5, which is less than the aforementioned determined conversion coefficient 10, then the safety status of the scan needs to be determined based on the current local volume SAR value. Even if the whole-body SAR value reaches its limit, the MRI scan can continue even if the local volume SAR value has not yet reached its own limit, as long as the local volume SAR value has not yet reached its own limit.

[0080] When the SAR value of the current local volume determined in step 82 reaches its upper limit, it is determined that there is a safety problem, and the magnetic resonance system can be controlled to stop the magnetic resonance scan.

[0081] If the result of step 81 is negative, the safety status of the magnetic resonance scan can be determined solely based on the current whole-body SAR value, i.e., whether the current whole-body SAR value has reached its own upper limit.

[0082] In the embodiments of this application, the limits for the ratio, the limits for the whole-body SAR value, and the limits for the local SAR value mentioned above can all be specified by safety standards in the field of magnetic resonance imaging, such as IEC standards. The upper limit of the ratio mentioned above is the ratio between the local SAR value and the whole-body SAR value.

[0083] like Figure 9 The diagram shown is a schematic diagram of a magnetic resonance system provided according to an embodiment of this application, including a body coil 91, a coupling coil 92, and a processor 93. Figure 9 The magnetic resonance system shown may include Figure 1 The magnetic resonance system and its variant structures shown may further include Figure 2The coupling coil is shown. This body coil 91 is used to transmit radio frequency excitation pulses, and its structure and working principle are similar to... Figure 1 The body coil 148 shown and Figure 2 The body coil 21 shown is similar. The coupling coil 92 is used to receive the radio frequency excitation pulse from the body coil 91 to generate a radio frequency field for exciting a local volume 950 of the scanned object. The structure, operating principle, and coupling method with the body coil of the coupling coil 92 can be compared with... Figure 2 The coupling coil 22 shown is similar. The processor 93 is used to execute the safety control method for magnetic resonance scanning in any of the above embodiments. Specifically, the processor 93 can be connected to... Figure 1 One or more of the image processor 128, array processor 139, system controller 130, and radio frequency transmission link shown are coupled.

[0084] Figure 10 A schematic diagram of the structure of a coupling coil according to another embodiment is shown, which can be used to perform magnetic resonance scanning, and the magnetic resonance scanning can be controlled via the safety control method provided in the embodiments of this application.

[0085] like Figure 10 As shown, the coupling coil includes a flexible main body 310 and an extension 320. The flexible main body 310 is deformable along a first direction to at least partially surround the area to be scanned (local volume) of the object, and the flexible main body 310 includes a main coil circuit 410.

[0086] The extension 320 is connected to the flexible main body 310. The extension 320 includes a compensation circuit 420, which is connected to the main body coil circuit 410 to form a first radio frequency transmitting coil. The compensation circuit 420 has a resonant frequency that is the same as the radio frequency transmitting frequency of the magnetic resonance system.

[0087] The electrical parameters of the main coil circuit 410 can be set so that it has the same resonant frequency. When it is connected to the compensation circuit 420, the compensation circuit 420 is actually equivalent to short-circuiting the main coil circuit 410 at the resonant frequency of the magnetic resonance system. Therefore, the compensation circuit 420 will not change the operating frequency of the main coil circuit because it is connected to the main coil circuit 410.

[0088] The aforementioned first direction can be the direction in which the flexible main body 310 is rolled (or bent) and unfolded approximately along an arc surface. For example, the flexible main body 310 can be unfolded into a sheet shape. When it is necessary to scan the area to be scanned using the coupling coil 300, one side of the sheet-shaped flexible main body 310 can be rolled towards the other side to at least partially surround (or cover, wrap) the area to be scanned, or both sides can be rolled towards each other simultaneously to form a generally cylindrical space therein to accommodate the area to be scanned.

[0089] An example of the first radio frequency transmitting coil described above is an orthogonal coil (e.g., the electrical structure of a birdcage coil). When the body coil has other electrical structures, the body coil circuit and the compensation circuit can also be designed to be connected to form such other electrical structures.

[0090] The extension 320 can fix the flexible main body 310 (for example, the extension can wrap around the neck, armpit or other body parts to prevent the flexible main body 310 from detaching from the shoulder), and the compensation circuit 420 in the extension 320 is connected to the main body coil circuit to form a first transmitting coil to compensate for the loss of parameters and performance caused by the incomplete closure of the flexible main body 310.

[0091] At least a portion of the extension 320 can be removed from the flexible body 310, so that the flexible body 310 can be used as a separate coupling coil.

[0092] In other words, at least a portion of the extension 320 is detachably connected to the flexible main body 310, and when the at least a portion of the extension 320 is not connected to the flexible main body 310, the main body coil circuit 410 and the compensation circuit 420 are electrically disconnected.

[0093] In the embodiments of this application, the flexible main body 310 may include, for example, an electrical inner layer and an outer wrapping layer. The main body coil circuit 410 may be disposed on the electrical inner layer, and the outer wrapping layer is used to provide insulation and protection for the circuit on the electrical inner layer.

[0094] Although this application describes Figure 2 , Figure 10 The coupling coil shown is illustrated; however, those skilled in the art will understand that the coupling coil used in the embodiments of this application may have other structures.

[0095] The above embodiments are merely illustrative examples of embodiments of this application, but this application is not limited thereto, and appropriate modifications can be made based on the above embodiments. For example, the above embodiments can be used alone, or one or more of the above embodiments can be combined.

[0096] The apparatus and methods described above in this application can be implemented in hardware or in combination with software. This application relates to a computer-readable program that, when executed by a logic component, enables the logic component to implement the apparatus or components described above, or to implement the various methods or steps described above. This application also relates to storage media for storing the above programs, such as hard disks, magnetic disks, optical disks, DVDs, flash memory, etc.

[0097] The methods / systems / apparatus described in conjunction with the embodiments of this application can be directly embodied in hardware, software modules executed by a processor, or a combination of both. For example, one or more and / or combinations of one or more functional block diagrams shown in the figures can correspond to various software modules in a computer program flow, or to various hardware modules. These software modules can correspond to the various steps shown in the figures. These hardware modules can be implemented, for example, using a field-programmable gate array (FPGA).

[0098] The software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. A storage medium can be coupled to the processor, enabling the processor to read information from and write information to the storage medium; or the storage medium can be an integral part of the processor. The processor and storage medium can reside in an ASIC. The software module can be stored in the memory of a mobile terminal or in a memory card that can be inserted into the mobile terminal. For example, if the device (such as a mobile terminal) uses a high-capacity MEGA-SIM card or a high-capacity flash memory device, the software module can be stored in the MEGA-SIM card or the high-capacity flash memory device.

[0099] One or more and / or one or more combinations of functional blocks described in the accompanying drawings can be implemented as a general-purpose processor, digital signal processor (DSP), application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, or any suitable combination thereof for performing the functions described herein. One or more and / or one or more combinations of functional blocks described in the accompanying drawings can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in communication with a DSP, or any other such configuration.

[0100] The present application has been described above with reference to specific embodiments. However, those skilled in the art should understand that these descriptions are exemplary and not intended to limit the scope of protection of the present application. Those skilled in the art can make various modifications and variations to the present application based on the principles thereof, and these modifications and variations are also within the scope of the present application.

Claims

1. A method of safety control of a magnetic resonance scan, wherein, The magnetic resonance scan uses a coupling coil for receiving radio frequency excitation pulses from a body coil of a magnetic resonance system to generate a radio frequency field for exciting a local volume of a scan object; The safety control method of the magnetic resonance scan comprises: acquiring a real-time monitored whole-body SAR value, wherein the whole-body SAR value is acquired based on the body coil; determining a conversion coefficient during the magnetic resonance scan, and converting the current whole-body SAR value into a current local SAR value of the local volume based on the conversion coefficient; and judging a safety state of the magnetic resonance scan based on the current local SAR value.

2. The method of claim 1, wherein, The conversion coefficient is acquired according to an electric field distribution in the magnetic resonance scan and a mass density distribution of the scan object, wherein the electric field distribution comprises an electric field distribution inside and outside the coupling coil, and the mass density distribution comprises a mass density inside the body coil and a mass density inside the coupling coil.

3. The method of claim 2, wherein, The conversion coefficient is obtained based on a first ratio and a second ratio, wherein: The first ratio is a ratio between an electric field inside the coupling coil volume and an electric field outside the coupling coil volume; and The second ratio is a ratio between a mass density inside the volume of the body coil and a mass density inside the volume of the coupling coil.

4. The method of claim 3, wherein, The conversion coefficient is a product of the first ratio and the second ratio.

5. The method of claim 3, wherein, The method further comprises: acquiring a first image signal and a second image signal in a pre-scan phase of the magnetic resonance scan, wherein the first image signal is an image signal inside the volume of the coupling coil, and the second image signal is an image signal outside the volume of the coupling coil, and acquiring a ratio between the first image signal and the second image signal as the first ratio.

6. The method of claim 5, wherein, In the pre-scan phase, a flip angle of the radio frequency excitation pulse is less than 30 degrees.

7. The method of claim 5, wherein, The pre-scan phase of the magnetic resonance scan acquires the first image signal and the second image signal using a gradient echo sequence.

8. The method of claim 1, wherein, Judging the safety state of the magnetic resonance scan based on the current SAR value of the local volume comprises: judging whether the conversion coefficient is greater than a preset upper limit of the ratio; and if the conversion coefficient is greater than the preset upper limit of the ratio, judging whether the current SAR value of the local volume reaches an upper limit value thereof.

9. A magnetic resonance scan system, comprising: a body coil for transmitting radio frequency excitation pulses; a coupling coil for receiving the radio frequency excitation pulses from the body coil to generate a radio frequency field for exciting a local volume of a scan object; and a processor for performing the safety control method of the magnetic resonance scan according to any one of claims 1 to 8. The coupling coil is arranged inside a volume formed by the body coil and is wirelessly coupled with the body coil.

10. The system of claim 9, wherein, ​

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