Eddy current measurement method and apparatus, electronic device, and storage medium

Abstract

The application provides a method for measuring eddy current, which comprises: applying a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection re-focusing gradient and a dispersion gradient to a preset region of a water phantom; the test gradient is used to generate eddy current; the radio frequency pulse signal is used to generate a magnetic resonance signal; the layer selection gradient is used to select the direction of the gradient magnetic field in the layer direction; the layer selection re-focusing gradient is used to re-focus the dispersion signal generated by the layer selection gradient; the dispersion gradient is used to disperse the excited residual magnetization vector; the water phantom is used to provide the magnetic resonance signal required by the eddy current measurement; the magnetic resonance signal generated by the radio frequency pulse signal in the preset region is collected, and the B0 eddy current and linear eddy current of the long time constant and short time constant eddy current are measured according to the magnetic resonance signal. The method for measuring eddy current provided by the application can completely measure all eddy current terms in one scan, and the sampling precision is high.

Description

Technical Field

[0001] This application relates to the field of eddy current measurement, and more specifically, to an eddy current measurement method, apparatus, electronic device, and storage medium. Background Technology

[0002] Magnetic resonance imaging (MRI) systems require rapid gradient switching during scanning, generating eddy currents in the surrounding conductors. These eddy currents vary with time and are spatially dependent, resulting in both spatially independent and spatially dependent eddy current terms. The spatially independent eddy current terms are called B0 eddy currents, while the eddy current terms dependent on spatial positions x, y, and z are called linear eddy currents.

[0003] Linear eddy currents can distort the actual gradient field, affecting the phase of the signal encoded by the gradient space, leading to image artifacts or signal inhomogeneity in the image. Furthermore, time-varying B0 eddy currents can cause the magnetic resonance imaging frequency to change over time, potentially producing severe off-resonance effects during imaging. For certain eddy current-sensitive sequences (such as Fast Spin Echo Imaging (FSE) and Diffusion Imaging Based on Echo Plane Acquisition (DWI), this can cause image artifacts, shifts, or even distortions.

[0004] Currently, the method for measuring eddy currents in magnetic resonance systems generally involves acquiring signals through a water model. This requires applying a test gradient, using a single 90° pulse to excite and acquire the free decay signal (FID). Because the phase of the FID signal is affected by the eddy currents, by applying and closing the test gradient, subtracting the phase of the FID signal yields the phase term affected only by the eddy currents, thus resolving the eddy current curve. However, this method cannot obtain groupings of long eddies, nor can it distinguish between direct and cross terms of the eddy currents.

[0005] Another eddy current measurement method based on multiple gradient echo (GRE) acquisition can measure cross terms and direct terms separately by applying readout gradients on different axes. In addition, multiple gradient echoes can measure the components of long eddies, but this method is difficult to measure short time constant eddies and cannot accurately reflect the size of the eddies at the sampling time. Summary of the Invention

[0006] The purpose of this application is to provide an eddy current measurement method, apparatus, electronic device, and storage medium. This method involves applying radio frequency pulse signals, test gradients, layer selection gradients, layer regrouping gradients, and dispersion gradients to a preset area of ​​a water model; acquiring the magnetic resonance signals generated by the radio frequency pulse signals in the preset area; and measuring the B0 eddy currents and linear eddy currents of long-time-constant and short-time-constant eddy currents based on the magnetic resonance signals. Using the eddy current measurement method provided by this application, the components of long eddy currents can be obtained in a single measurement, the direct and cross terms of eddy currents can be distinguished, and the accuracy of eddy current measurement can be improved.

[0007] In a first aspect, embodiments of this application provide an eddy current measurement method, the method comprising: applying a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection convergence gradient, and a dispersion gradient to a preset region of a water model; wherein, the test gradient is used to generate eddy currents; the radio frequency pulse signal is used to generate magnetic resonance signals; the layer selection gradient is used to select the direction of the gradient magnetic field in the layer direction; the layer selection convergence gradient is used to converge the dephased signals generated by the layer selection gradient; the dispersion gradient is used to disperse the excited residual magnetization vector; and the water model is used to provide the magnetic resonance signals required for eddy current measurement. The magnetic resonance signals generated by the radio frequency pulse signal in the preset region are acquired, and the B0 eddy currents and linear eddy currents of long-time constant and short-time constant eddy currents are measured based on the magnetic resonance signals; wherein, the B0 eddy currents are spatially independent eddy currents; the linear eddy currents are first-order eddy currents in the magnetic resonance signals that are spatially dependent; and the magnetic resonance signals include the magnetic resonance signals generated by the radio frequency pulse signal in the preset region.

[0008] In the above implementation process, radio frequency pulse signals, test gradients, layer selection gradients, layer selection regrouping gradients, and dispersion gradients are applied to a preset area of ​​the water model. Furthermore, the magnetic resonance signal generated by the radio frequency pulse signal in the preset area is acquired, and the B0 eddy current and linear eddy current of the long-time constant eddy current and the short-time constant eddy current are measured based on the magnetic resonance signal. Thus, the direct and cross terms of all eddy currents are measured in a single complete measurement; this improves both testing efficiency and accuracy.

[0009] Optionally, in this embodiment, the test gradient includes a first test gradient and a second test gradient with opposite polarities; the magnetic resonance signal includes a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal. Applying the radio frequency pulse signal, the test gradient, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient to the preset region of the water model includes: applying the first test gradient to the preset region, then applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient to the preset region of the water model; applying the second test gradient to the preset region, then applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient to the preset region of the water model. The process involves acquiring magnetic resonance signals generated by radio frequency pulse signals within a preset region, and measuring the B0 eddy current and linear eddy current of long-time constant and short-time constant eddy currents based on the magnetic resonance signals. This includes: acquiring a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal within the preset region; wherein the first and second magnetic resonance signals include magnetic resonance signals corresponding to a first test gradient; the third and fourth magnetic resonance signals include magnetic resonance signals corresponding to a second test gradient; and calculating the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals.

[0010] In the above implementation process, the eddy current measurement method provided in this application applies a test gradient and a radio frequency pulse signal, a layer selection gradient, a layer selection regrouping gradient, and a dispersion gradient to the preset area of ​​the water model twice, but the test gradients used in these two applications are test gradients with opposite polarities. First and third magnetic resonance signals are collected in the first preset area of ​​the water model, respectively; second and fourth magnetic resonance signals are collected in the second preset area of ​​the water model, respectively. Based on the collected first, second, third, and fourth magnetic resonance signals, the B0 eddy current and linear eddy current of the long-time constant eddy current are calculated; therefore, using the eddy current measurement method provided in this application can avoid the influence of other signals on the phase.

[0011] Optionally, in this embodiment, the layer selection gradient includes a first layer selection gradient and a second layer selection gradient with opposite polarities; the layer selection re-convergence gradient includes a first layer selection re-convergence gradient and a second layer selection re-convergence gradient with opposite polarities; the preset region includes a first preset region and a second preset region. After applying the first test gradient to the preset region, applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersive gradient to the preset region of the water model includes: after applying the test gradient to the first preset region, applying the radio frequency pulse signal, the first layer selection gradient, the first layer selection re-convergence gradient, and the dispersive gradient to the first preset region of the water model, and acquiring a first magnetic resonance signal of the first preset region; wherein, the test gradient is located on the same gradient axis as the first layer selection gradient and the first layer selection re-convergence gradient; after applying the first test gradient to the second preset region, applying the radio frequency pulse signal, the second layer selection gradient, the second layer selection re-convergence gradient, and the dispersive gradient to the second preset region of the water model, and acquiring a second magnetic resonance signal of the second preset region; wherein, the test gradient is located on the same gradient axis as the second layer selection gradient and the second layer selection re-convergence gradient. The calculation of the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals includes: acquiring the first, second, third, and fourth magnetic resonance signals; and calculating the direct terms of the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals.

[0012] In the above implementation process, after measuring the first magnetic resonance signal excited by the radio frequency pulse, a layer selection gradient and a layer selection retraction gradient with opposite polarities to the layer selection gradient and the layer selection retraction gradient can be applied to the second preset region of the water model; thereby obtaining the second magnetic resonance signal. The phase difference between the first magnetic resonance signal and the second magnetic resonance signal is used as the basis for calculating the long time constant eddy current and the short time constant eddy current, thereby canceling out other factors that affect the phase in the measurement, such as the phase change caused by the B0 offset.

[0013] Optionally, in this embodiment, after applying the first test gradient to the preset region, applying the radio frequency pulse signal, layer selection gradient, layer selection re-convergence gradient, and dispersion gradient to the preset region of the water model further includes: after applying the test gradient to the first preset region, applying the radio frequency pulse signal, the first layer selection gradient, the first layer selection re-convergence gradient, and dispersion gradient to the first preset region of the water model, and acquiring the first magnetic resonance signal of the first preset region; wherein the test gradient is located on a different gradient axis than the first layer selection gradient and the first layer selection re-convergence gradient; after applying the first test gradient to the second preset region, applying the radio frequency pulse signal, the second layer selection gradient, the second layer selection re-convergence gradient, and dispersion gradient to the second preset region of the water model, and acquiring the second magnetic resonance signal of the second preset region; wherein the test gradient is located on a different gradient axis than the second layer selection gradient and the second layer selection re-convergence gradient. The calculation of the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals includes: acquiring the first, second, third, and fourth magnetic resonance signals; and calculating the cross term of the linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals.

[0014] In the above implementation process, after applying a test gradient to the preset area of ​​the water model, a test gradient, an RF pulse signal, a layer selection gradient, and a layer selection retraction gradient are applied; and the test gradient, the layer selection gradient, and the layer selection retraction gradient are located on different gradient axes; thereby accurately measuring the cross term of the long-time constant eddy current.

[0015] Optionally, in this embodiment, after applying a test gradient to a first preset region, an RF pulse signal, a first layer selection gradient, a first layer selection retraction gradient, and a dispersion gradient are applied to the first preset region of the water model, and a first magnetic resonance signal of the first preset region is acquired; wherein, the test gradient being located on different gradient axes from the first layer selection gradient and the first layer selection retraction gradient includes: after applying the first test gradient to the first gradient axis, an RF pulse signal, a first layer selection gradient, a first layer selection retraction gradient, and a dispersion gradient are applied to a second gradient axis; wherein, the first gradient axis and the second gradient axis are X gradient axes, Y gradient axes, or Z gradient axes, and the first gradient axis and the second gradient axis are not simultaneously the same gradient axis. Calculating the cross term of the time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal includes: calculating the cross term of the first gradient axis and the second gradient axis of the time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal.

[0016] In the above implementation process, when measuring the cross-terms of long-time constant eddies, a test gradient is applied to the X-axis, and then a layer-selective gradient and a layer-selective retraction gradient are applied to the Y-axis; magnetic resonance signals are acquired within a preset region. Further, the long-time constant eddies are obtained from the magnetic resonance signals, and the XY cross-terms of the long-time constant eddies are obtained from the long-time constant eddies. By applying the test gradient, layer-selective gradient, and layer-selective retraction gradient in this way, the measurement of different cross-terms of the eddies can be achieved. This method is also applicable to the measurement of cross-terms of short-time constant eddies.

[0017] Optionally, in this embodiment of the application, after calculating the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal, the method further includes: repeating the method after a certain time interval to obtain the B0 eddy current and linear eddy current of the long-time constant eddy current at multiple different time points.

[0018] In the above implementation process, for long-time constant eddy current measurement, the signal acquisition module can be repeatedly applied; radio frequency pulses, layer selection gradient G1 and layer selection back-convergence gradient G2 are acquired to obtain eddy current values ​​at different time points: t1, t2, t3, t4... The time between each dashed box can be the same or different. In order to save the amount of measurement data (number of measurements), the signal acquisition module can use logarithmic processing in the time interval, that is, the time interval is shorter when t is shorter, and the time resolution of eddy current measurement is higher; the time interval is longer when t is longer, which reduces the time of eddy current measurement and also has high resolution.

[0019] Optionally, in this embodiment, applying a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection re-convergence gradient, and a dispersion gradient to a preset region of the water model includes: after applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient, applying a first test gradient to the preset region of the water model; after applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient, applying a second test gradient to the preset region of the water model. Acquiring the magnetic resonance signal generated by the radio frequency pulse signal in the preset region, and measuring the B0 eddy current and linear eddy current of the long time constant and short time constant eddy currents based on the magnetic resonance signal includes: acquiring a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal in the preset region; wherein the first and second magnetic resonance signals include magnetic resonance signals corresponding to the first test gradient; the third and fourth magnetic resonance signals include magnetic resonance signals corresponding to the second test gradient; and calculating the B0 eddy current and linear eddy current of the short time constant eddy current based on the first, second, third, and fourth magnetic resonance signals.

[0020] In the above implementation process, the eddy current measurement method provided in the application embodiment applies a radio frequency pulse signal, a layer selection gradient, a layer selection reconvergence gradient, a dispersion gradient, and a test gradient to the preset area of ​​the water model twice, but the test gradients used in these two instances are test gradients with opposite polarities. First and third magnetic resonance signals are acquired in the first preset area of ​​the water model, respectively; second and fourth magnetic resonance signals are acquired in the second preset area of ​​the water model, respectively. Based on the acquired first, second, third, and fourth magnetic resonance signals, the B0 eddy current and linear eddy current of the short-time constant eddy current are calculated, enabling accurate measurement of the B0 eddy current and linear eddy current of the short-time constant.

[0021] Secondly, embodiments of this application provide an eddy current measurement device, which includes: a signal application module, a signal acquisition module, and an eddy current measurement module. The signal application module is used to apply a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection regrouping gradient, and a dispersion gradient to a preset area of ​​a water model; wherein, the test gradient is used to generate eddy currents; the radio frequency pulse signal is used to generate magnetic resonance signals; the layer selection gradient is used to select the direction of the gradient magnetic field in the layer direction; the layer selection regrouping gradient is used to regroup the dephasing signals generated by the layer selection gradient; the dispersion gradient is used to disperse the excited residual magnetization vector; the water model is used to provide the magnetic resonance signals required for eddy current measurement; the signal acquisition module is used to acquire the magnetic resonance signals generated by the radio frequency pulse signal in the preset area; the eddy current measurement module is used to measure the B0 eddy current and linear eddy current of long-time constant and short-time constant eddy currents respectively based on the magnetic resonance signals; wherein, the B0 eddy current is an eddy current independent of spatial position; the linear eddy current is a first-order eddy current in the magnetic resonance signal that is spatially related; the magnetic resonance signal includes the magnetic resonance signal generated by the radio frequency pulse signal in the preset area.

[0022] Thirdly, embodiments of this application provide an electronic device, which includes a memory and a processor. The memory stores program instructions, and when the processor reads and runs the program instructions, it executes the steps in any of the above implementation methods.

[0023] Fourthly, embodiments of this application also provide a computer-readable storage medium storing computer program instructions, which, when read and executed by a processor, perform the steps in any of the above implementations. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a flowchart of eddy current measurement provided in an embodiment of this application;

[0026] Figure 2 A schematic diagram of a water model provided in an embodiment of this application;

[0027] Figure 3 A flowchart illustrating the measurement process of B0 eddy current and linear eddy current for long-time constant eddy currents provided in this application embodiment;

[0028] Figure 4 A flowchart illustrating the measurement process of the direct terms of the B0 eddy current and the linear eddy current for a long-time constant eddy current, as provided in this application embodiment.

[0029] Figure 5 A schematic diagram of the measurement of B0 eddy current and direct term of long-time constant eddy current provided in an embodiment of this application;

[0030] Figure 6 A flowchart illustrating the measurement of the cross term of a linear eddy current in a long-time constant eddy current, as provided in an embodiment of this application.

[0031] Figure 7 A schematic diagram of the measurement of the long-time constant eddy current cross term provided in an embodiment of this application;

[0032] Figure 8 A schematic diagram of the measurement of B0 eddy current and linear eddy current of short time constant eddy current provided in the embodiments of this application;

[0033] Figure 9 A schematic diagram illustrating the direct terms of short-time constant eddy current B0 and linear eddy current provided for embodiments of this application;

[0034] Figure 10 A schematic diagram of the cross term of a short-time-constant linear eddy current provided in an embodiment of this application;

[0035] Figure 11 This is a schematic diagram of alternating sampling provided in an embodiment of this application;

[0036] Figure 12 This is a schematic diagram of the eddy current measurement device provided in the embodiments of this application;

[0037] Figure 13This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will now be described with reference to the accompanying drawings. For example, the flowcharts and block diagrams in the drawings illustrate the architecture, functions, and operations of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, program segment, or part of code, which contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, and combinations of blocks in the block diagram and / or flowchart, can be implemented using a dedicated hardware-based system that performs the specified function or action, or can be implemented using a combination of dedicated hardware and computer instructions. In addition, the functional modules in the various embodiments of the present invention may be integrated together to form an independent part, or each module may exist separately, or two or more modules may be integrated to form an independent part.

[0039] During the research process, the applicant discovered that by first applying a test gradient, and then using a single 90° pulse to excite and acquire the free decay signal (FID), because the phase of the FID signal is affected by eddy currents, by applying and closing the test gradient, the phase of the FID signal can be subtracted to obtain the phase term affected only by eddy currents, thus resolving the eddy current curve. However, this method has two drawbacks: firstly, because the FID signal decays rapidly, it is impossible to measure the components of long eddy currents; secondly, the direct and cross terms of the eddy currents are superimposed on the phase of the FID signal, making it impossible to distinguish between the direct and cross terms in measurement.

[0040] Another eddy current measurement method based on multiple gradient echo (GRE) acquisition can measure cross-terms and direct terms separately by applying readout gradients on different axes. In addition, multiple gradient echoes can measure the components of long eddies. However, this method has the following two problems: First, for eddies with short time constants, a high time resolution (50-200µs) is required, but the repetition time (TR) of each gradient echo is relatively long (TR is about 10-20ms), and TR determines the time resolution, making it difficult to measure short time constant eddies. Second, the eddy current value at each measurement time point is the average value of the echo time (TE) and cannot accurately reflect the size of the eddy current at the sampling time.

[0041] Based on this, embodiments of this application provide an eddy current measurement method and apparatus. A test gradient, a radio frequency pulse signal, a layer selection gradient, and a layer selection reconvergence gradient are applied to a preset area in a water model imaging system. The magnetic resonance signal generated by the radio frequency pulse signal in the preset area is acquired, and the B0 eddy current and linear eddy current of long-time constant and short-time constant eddy currents are measured based on the magnetic resonance signal. This allows for the measurement of all eddy current components (including long-time constant and short-time constant eddy currents) in a single complete measurement, improving time accuracy and solving the problem of inaccurate eddy current measurement.

[0042] Please refer to Figure 1 , Figure 1 This is a flowchart of eddy current measurement provided for an embodiment of this application.

[0043] Please refer to the following: Figure 2 , Figure 2 This is a schematic diagram of a water model provided in an embodiment of this application; Figure 2 The water model shown contains a first layer and a second layer. Here, the first layer is the first preset region in this embodiment, and the second layer is the second preset region in this embodiment; both the first layer and the second layer are distanced from the center by a distance D. r Correspondingly, in the embodiments of this application, the magnetic resonance signals generated by the radio frequency pulse signal in the first preset region are the first magnetic resonance signal and the third magnetic resonance signal, and the magnetic resonance signals generated by the radio frequency pulse signal in the second preset region are the second magnetic resonance signal and the fourth magnetic resonance signal.

[0044] It should be noted that the diameter of the water model used in this embodiment is between 10cm and 20cm, and the T1 / T2 ratio of the water model solution is within 100ms. However, the size of the water model and the T1 / T2 value of the water model solution can be adaptively adjusted in practical applications. The size of the water model and the T1 / T2 value of the water model solution given in this embodiment are merely exemplary and should not be construed as limiting the scope of protection of this embodiment. Wherein, T1 is the longitudinal relaxation time of the water model aqueous solution; T2 is the transverse relaxation time of the water model aqueous solution.

[0045] The eddy current measurement method includes:

[0046] Step S100: Apply radio frequency pulse signal, test gradient, select layer gradient, select layer back-convergence gradient and disperse gradient to the preset area of ​​the water model.

[0047] In step S100 above, a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection retraction gradient, and a dispersion gradient are applied to a preset area of ​​the water model. It should be noted that the contents to be measured in this embodiment include the B0 term of the long-time constant eddy current, the direct term of the long-time constant eddy current, the cross term of the long-time constant eddy current, the B0 term of the short-time constant eddy current, the direct term of the short-time constant eddy current, and the cross term of the short-time constant eddy current. When measuring different contents, the polarity of the test gradient, the layer selection gradient, and the layer selection retraction gradient may be different; and the gradient axis of the test gradient and other signals may also be different.

[0048] Those skilled in the art will understand that the test gradient is used to generate eddy currents; the radio frequency pulse signal is used to generate magnetic resonance signals; the layer selection gradient is used to select the direction of the gradient magnetic field in the layer direction; the layer selection convergence gradient is used to converge the dephased signal generated by the layer selection gradient; the dispersion gradient is used to disperse the excited residual magnetization vector; and the water model is used to provide the magnetic resonance signal required for eddy current measurement.

[0049] Step S101: Acquire the magnetic resonance signal generated by the radio frequency pulse signal in the preset area, and measure the B0 eddy current and linear eddy current of the long time constant eddy current and the short time constant eddy current according to the magnetic resonance signal.

[0050] In step S101 above, the magnetic resonance signal generated by the radio frequency pulse signal in the preset area is collected respectively; the B0 eddy current and linear eddy current of the long time constant eddy current and the short time constant eddy current are measured according to the magnetic resonance signal.

[0051] It should be noted that B0 eddy currents are eddy currents independent of spatial location; linear eddy currents are first-order eddy currents in magnetic resonance signals that are spatially dependent; and magnetic resonance signals include magnetic resonance signals generated by radio frequency pulse signals in a preset region.

[0052] pass Figure 1 As can be seen, a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection regrouping gradient, and a dispersion gradient are applied to a preset area of ​​the water model. Furthermore, the magnetic resonance signal generated by the radio frequency pulse signal in the preset area is acquired, and the B0 eddy current and linear eddy current of the long-time constant eddy current and the short-time constant eddy current are measured based on the magnetic resonance signal. Thus, the direct and cross terms of all eddy currents are measured in a single complete measurement; this improves both testing efficiency and accuracy.

[0053] Please refer to Figure 3 , Figure 3This application provides a flowchart for measuring B0 eddies and linear eddies in long-time constant eddies according to embodiments of the present application. The test gradients provided in this application include a first test gradient and a second test gradient, with opposite polarities. Magnetic resonance signals include a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal; the first and second magnetic resonance signals include magnetic resonance signals corresponding to the first test gradient; the third and fourth magnetic resonance signals include magnetic resonance signals corresponding to the second test gradient. The first and third magnetic resonance signals are both generated in a first preset region of the water model, and the second and fourth magnetic resonance signals are both generated in a second preset region of the water model.

[0054] Step S200: After applying the first test gradient to the preset area, apply the radio frequency pulse signal, the layer selection gradient, the layer selection re-aggregation gradient and the dispersion gradient to the preset area of ​​the water model.

[0055] In step S200 above, a first test gradient is first applied to a preset area of ​​the water model; further, a radio frequency pulse signal, a layer selection gradient, a layer selection re-aggregation gradient, and a dispersion gradient are applied to the same preset area.

[0056] Step S201: After applying the second test gradient to the preset area, apply the radio frequency pulse signal, the layer selection gradient, the layer selection re-aggregation gradient and the dispersion gradient to the preset area of ​​the water model.

[0057] In step S201 above, a second test gradient is first applied to a preset area of ​​the water model; further, a radio frequency pulse signal, a layer selection gradient, a layer selection re-aggregation gradient, and a dispersion gradient are applied to the same preset area.

[0058] It is worth noting that the polarities of the first test gradient and the second test gradient are opposite; for example, if the first test gradient applied in step S200 is G1, then the second test gradient applied in step S201 is -G1.

[0059] Step S202: Acquire the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal in the preset area.

[0060] In step S202 above, a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal are collected in a preset area. It should be noted that the first magnetic resonance signal and the third magnetic resonance signal are collected in the first preset area of ​​the water model, and the second magnetic resonance signal and the fourth magnetic resonance signal are collected in the second preset area of ​​the water model.

[0061] In this embodiment, the first, second, third, and fourth magnetic resonance signals are used only to distinguish differences in test gradients and preset regions, and do not represent that they are the same signals in different measurements. For example, when measuring a B0 eddy current with a long time constant, the first magnetic resonance signal collected in the first preset region; and when measuring a B0 eddy current with a short time constant, the first magnetic resonance signal collected in the first preset region; are not completely identical magnetic resonance signals in the two measurements, and the data from the two measurements are not interchangeable. In this embodiment, the first, second, third, and fourth magnetic resonance signals are only used to distinguish differences in test gradients and preset regions.

[0062] Step S203: Calculate the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0063] In step S203 above, the B0 eddy current and linear eddy current of the long-time constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal collected.

[0064] pass Figure 3 As can be seen, the eddy current measurement method provided in this application applies a test gradient and a radio frequency pulse signal, a layer selection gradient, a layer selection regrouping gradient, and a dispersion gradient to the preset area of ​​the water model twice, but the test gradients used in these two applications are test gradients with opposite polarities. First and third magnetic resonance signals are collected in the first preset area of ​​the water model, respectively; second and fourth magnetic resonance signals are collected in the second preset area of ​​the water model, respectively. Based on the collected first, second, third, and fourth magnetic resonance signals, the B0 eddy current and linear eddy current of the long-time constant eddy current are calculated; therefore, the eddy current measurement method provided in this application can avoid the influence of other signals on the phase.

[0065] Please refer to Figure 4 , Figure 4 This application provides a flowchart for measuring the direct terms of B0 eddies and linear eddies in a long-time constant eddy current. The layer selection gradients provided in this application include a first layer selection gradient and a second layer selection gradient with opposite polarities; the layer selection convergence gradients include a first layer selection convergence gradient and a second layer selection convergence gradient with opposite polarities; the preset regions include a first preset region and a second preset region, which correspond to the first and second layers of the water model, respectively.

[0066] Please refer to the following: Figure 5 , Figure 5This is a schematic diagram illustrating the measurement of the B0 eddy current and direct term of a long-time constant eddy current provided in an embodiment of this application; Figure 5 In the diagram, G0 is the test gradient, G1 is the layer selection gradient, G2 is the layer selection back-aggregation gradient, DAQ is the signal acquisition gradient, and G3 is the scattering gradient.

[0067] The method includes:

[0068] Step S300: After applying the first test gradient to the first preset region, apply the radio frequency pulse signal, the first layer selection gradient, the first layer re-convergence gradient and the dispersion gradient to the first preset region of the water model, and obtain the first magnetic resonance signal of the first preset region.

[0069] In step S300 above, such as Figure 5 As shown, firstly, a first test gradient G0 is applied to a first preset region, and then an RF pulse signal, a first layer selection gradient G1, a first layer selection re-convergence gradient G2, and a dispersion gradient G3 are applied to the first preset region of the water model. It is particularly important to emphasize that the test gradient G0 is located on the same gradient axis as the first layer selection gradient G1 and the first layer selection re-convergence gradient G2.

[0070] Step S301: After applying the first test gradient to the second preset region, apply the radio frequency pulse signal, the second layer selection gradient, the second layer re-convergence gradient and the dispersion gradient to the second preset region of the water model, and obtain the second magnetic resonance signal of the second preset region.

[0071] In step S301 above, firstly, a first test gradient G0 is applied to the second preset region, and then an RF pulse signal, a second layer selection gradient -G1, a second layer selection re-convergence gradient -G2, and a dispersive gradient G3 are applied to the second preset region of the water model. It is particularly important to emphasize that the test gradient G0, the second layer selection gradient -G1, and the second layer selection re-convergence gradient -G2 are located on the same gradient axis; the first layer selection gradient G1 and the second layer selection gradient -G1 have opposite polarities, and the first layer selection re-convergence gradient G2 and the second layer selection re-convergence gradient -G2 have opposite polarities.

[0072] In an optional embodiment, after applying a second test gradient -G0 to a first preset region, a radio frequency pulse signal, a first layer selection gradient G1, a first layer selection re-convergence gradient G2, and a dispersion gradient are applied to the first preset region of the water phantom. It is particularly important to emphasize that the test gradient, the first layer selection gradient G1, and the first layer selection re-convergence gradient G2 are located on the same gradient axis; further, a third magnetic resonance signal is acquired.

[0073] A second test gradient -G0 is applied to a second preset region, followed by an RF pulse signal, a second layer selection gradient -G1, a second layer selection retraction gradient -G2, and a dispersion gradient to the second preset region of the water phantom. It is particularly important to emphasize that the test gradient, the second layer selection gradient -G1, and the second layer selection retraction gradient -G2 are located on the same gradient axis; the first layer selection gradient G1 and the second layer selection gradient -G1 have opposite polarities, as do the first layer selection retraction gradient G2 and the second layer selection retraction gradient -G2; furthermore, a fourth magnetic resonance signal is acquired.

[0074] Step S302: Acquire the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0075] Step S303: Calculate the B0 eddy current and the direct term of the linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0076] In steps S302-S303 above, the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal are acquired, and the B0 eddy current and the direct term of the linear eddy current of the long time constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0077] For example, the phase difference between the two acquisitions can eliminate term B0, as follows:

[0078]

[0079] The sum of the phases from the two acquisitions can eliminate the linear eddy current term, as follows:

[0080]

[0081] Where γ is the magnetic resonance gyrometry, g r b0(t) is the linear eddy current term excited by the test gradient, and b0(t) is the B0 eddy current term.

[0082] Repeat the above steps, applying a second test gradient -G0 (with the same amplitude but opposite polarity), to obtain the phase difference between the second set of signals acquired from the first and second layers:

[0083]

[0084] The sum of the phases from the two acquisitions is:

[0085]

[0086] Depend on and Calculation yields:

[0087]

[0088]

[0089] k r (t) is the integral of the linear eddy current over time, with respect to k. r The eddy current g can be obtained by differentiating (t) over time. r (t). k B0 (t) is the integral of the B0 eddy current over time, with respect to k. B0 By performing time differentiation on (t), the eddy current b0(t) can be obtained.

[0090] pass Figure 4 and Figure 5 It can be seen that after measuring the first magnetic resonance signal excited by the radio frequency pulse, a layer selection gradient and a layer selection retraction gradient with opposite polarities to the layer selection gradient and the layer selection retraction gradient can be applied to the second preset region of the water model; thereby obtaining the second magnetic resonance signal. The phase difference between the first magnetic resonance signal and the second magnetic resonance signal is used as the basis for calculating the long time constant eddy current and the short time constant eddy current, thereby canceling out other factors that affect the phase in the measurement, such as the phase change caused by the B0 offset.

[0091] Please refer to Figure 6 , Figure 6 A flowchart illustrating the measurement process of the cross-terms of a linear eddy current with a long-time constant eddy current, as provided in this application embodiment; please refer to [link / reference needed]. Figure 7 , Figure 7 This is a schematic diagram of the measurement of the long-time constant eddy current cross term provided in an embodiment of this application; Figure 7 In the diagram, G0 is the test gradient, G1 is the layer selection gradient, G2 is the layer selection back-aggregation gradient, DAQ is the signal acquisition gradient, and G3 is the scattering gradient.

[0092] Step S400: After applying the test gradient to the first preset region, apply the radio frequency pulse signal, the first layer selection gradient, the first layer re-convergence gradient and the dispersion gradient to the first preset region of the water model, and obtain the first magnetic resonance signal of the first preset region.

[0093] In step S400 above, such as Figure 7 As shown, firstly, a first test gradient G0 is applied to a first preset region, and then an RF pulse signal, a first layer selection gradient G1, a first layer selection re-convergence gradient G2, and a dispersion gradient G3 are applied to the first preset region of the water model. It is particularly important to emphasize that the test gradient G0 is located on a different gradient axis than the first layer selection gradient G1 and the first layer selection re-convergence gradient G2.

[0094] Step S401: After applying the first test gradient to the second preset region, apply the radio frequency pulse signal, the second layer selection gradient, the second layer re-convergence gradient and the dispersion gradient to the second preset region of the water model, and obtain the second magnetic resonance signal of the second preset region.

[0095] In step S401 above, firstly, a first test gradient G0 is applied to the second preset region, and then an RF pulse signal, a second layer selection gradient -G1, a second layer selection re-convergence gradient -G2, and a dispersion gradient G3 are applied to the second preset region of the water model. It is particularly important to emphasize that the test gradient G0 is located on a different gradient axis than the second layer selection gradient -G1 and the second layer selection re-convergence gradient -G2; the polarities of the first layer selection gradient G1 and the second layer selection gradient -G1 are opposite, and the polarities of the first layer selection re-convergence gradient G2 and the second layer selection re-convergence gradient -G2 are also opposite.

[0096] In an optional embodiment, a second test gradient -G0 is first applied to a first preset region, followed by an RF pulse signal, a first layer selection gradient G1, a first layer selection re-convergence gradient G2, and a dispersion gradient to the first preset region of the water phantom. It is particularly important to emphasize that the test gradient is located on a different gradient axis than the first layer selection gradient G1 and the first layer selection re-convergence gradient G2; further, a third magnetic resonance signal is acquired.

[0097] First, a second test gradient -G0 is applied to the second preset region. Then, a radio frequency pulse signal, a second layer selection gradient -G1, a second layer selection retraction gradient -G2, and a dispersion gradient are applied to the second preset region of the water phantom. It is particularly important to emphasize that the test gradient is located on a different gradient axis than the second layer selection gradient -G1 and the second layer selection retraction gradient -G2; the first layer selection gradient G1 and the second layer selection gradient -G1 have opposite polarities, as do the first layer selection retraction gradient G2 and the second layer selection retraction gradient -G2; furthermore, a fourth magnetic resonance signal is acquired.

[0098] Step S402: Acquire the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0099] Step S403: Calculate the cross term of the linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0100] In steps S402-S403 above, the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal are acquired, and the cross term of the linear eddy current of the long time constant eddy current is calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0101] pass Figure 6 and Figure 7It can be seen that after applying the test gradient to the preset area of ​​the water model, the test gradient, the radio frequency pulse signal, the layer selection gradient, and the layer selection retraction gradient are applied; and the test gradient, the layer selection gradient, and the layer selection retraction gradient are located on different gradient axes; thus, the cross term of the time constant eddy current is accurately measured.

[0102] In an optional embodiment, after applying a first test gradient to a first gradient axis, a radio frequency pulse signal, a first layer selection gradient, a first layer selection reconvergence gradient, and a scattering gradient are applied to a second gradient axis; wherein the first gradient axis and the second gradient axis are X-axis, Y-axis, or Z-axis, and the first gradient axis and the second gradient axis are not simultaneously the same gradient axis. Further, the first gradient axis and second gradient axis intersection term of the time-constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal.

[0103] For example, after applying the test gradient G0 to a preset region of the water model, applying the radio frequency pulse signal, the layer selection gradient G1, and the layer selection retraction gradient G2 to the preset region of the water model includes: applying the test gradient G0 to the X gradient axis, applying the layer selection gradient G1 and the layer selection retraction gradient G2 to the Y gradient axis; acquiring the first magnetic resonance signal and the second magnetic resonance signal within the preset region, and obtaining the long-time constant eddy current excited by the test gradient based on the magnetic resonance signal; and obtaining the XY cross term of the long-time constant eddy current based on the long-time constant eddy current. Similarly, applying G0 to the X-axis and G1 / G2 to the Z-axis allows for the measurement of the linear eddy current cross term XZ; applying G0 to the Y-axis and G1 / G2 to the X-axis allows for the measurement of the linear eddy current cross term YX; applying G0 to the Y-axis and G1 / G2 to the Z-axis allows for the measurement of the linear eddy current cross term YZ; applying G0 to the Z-axis and G1 / G2 to the X-axis allows for the measurement of the linear eddy current cross term ZX; applying G0 to the Z-axis and G1 / G2 to the Y-axis allows for the measurement of the linear eddy current cross term ZY. The above methods are also applicable to the cross term of eddy currents with a time constant during the test period.

[0104] Therefore, when measuring the cross-terms of long-time constant eddies, if a test gradient is applied to the X-axis, and then a layer-selective gradient and a layer-selective retraction gradient are applied to the Y-axis, and magnetic resonance signals are acquired within a preset region, the long-time constant eddies can be obtained from the magnetic resonance signals, and the XY cross-terms of the long-time constant eddies can be obtained from the long-time constant eddies. By applying the test gradient, layer-selective gradient, and layer-selective retraction gradient in this way, different cross-terms of the eddies can be measured, and this method is also applicable to the measurement of cross-terms of short-time constant eddies.

[0105] In an alternative embodiment, please continue to refer to Figure 5 and Figure 7After calculating the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal, the method further includes: repeating the method after a certain time interval to obtain the B0 eddy current and linear eddy current of the long-time constant eddy current at multiple different time points.

[0106] Therefore, for long-time constant eddy current measurements, the signal acquisition module can be repeatedly applied multiple times. Figure 5 and Figure 7 (Dashed box in the middle); radio frequency pulse, layer selection gradient G1 and layer selection back convergence gradient G2 and acquisition, can obtain eddy current values ​​at different time points: t1, t2, t3, t4... The time between each dashed box can be the same or different. In order to save the amount of measurement data (number of measurements), the signal acquisition module can use logarithmic processing in the time interval, that is, the time interval is shorter when t is shorter, the time resolution of eddy current measurement is higher, and the time interval is longer when t is longer, reducing the time of eddy current measurement and maintaining high resolution.

[0107] Please refer to Figure 8 , Figure 8 A schematic diagram of the measurement of B0 eddy current and linear eddy current in a short-time constant eddy current provided in an embodiment of this application; the method includes:

[0108] Step S500: After applying the radio frequency pulse signal, the layer selection gradient, the layer regrouping gradient and the dispersion gradient, the first test gradient is then applied to the preset area of ​​the water model.

[0109] In step S500 above, a radio frequency pulse signal, a layer selection gradient, a layer selection re-aggregation gradient, and a dispersion gradient are first applied to a preset area of ​​the water model; further, a first test gradient is applied to the same preset area.

[0110] Step S501: After applying the radio frequency pulse signal, the layer selection gradient, the layer regrouping gradient and the dispersion gradient, apply the second test gradient to the preset area to the preset area of ​​the water model.

[0111] In step S501 above, a radio frequency pulse signal, a layer selection gradient, a layer selection re-aggregation gradient, and a dispersion gradient are first applied to a preset area of ​​the water model; further, a second test gradient is applied to the same preset area.

[0112] It is worth noting that the polarities of the first and second test gradients mentioned above are opposite.

[0113] Step S502: Acquire the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal in the preset area.

[0114] In step S502 above, a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal are collected in a preset area. It should be noted that the first magnetic resonance signal and the third magnetic resonance signal are collected in the first preset area of ​​the water model, and the second magnetic resonance signal and the fourth magnetic resonance signal are collected in the second preset area of ​​the water model.

[0115] Step S503: Calculate the B0 eddy current and linear eddy current of the short time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0116] In step S503 above, the B0 eddy current and linear eddy current of the short time constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal collected.

[0117] pass Figure 8 As can be seen, the eddy current measurement method provided in the application embodiment applies a radio frequency pulse signal, a layer selection gradient, a layer selection reconvergence gradient, a dispersion gradient, and a test gradient to a preset area of ​​the water model twice, but the test gradients used in these two applications are test gradients with opposite polarities. A first magnetic resonance signal and a third magnetic resonance signal are collected in the first preset area of ​​the water model, respectively; a second magnetic resonance signal and a fourth magnetic resonance signal are collected in the second preset area of ​​the water model, respectively. Based on the collected first, second, third, and fourth magnetic resonance signals, the B0 eddy current and linear eddy current of the short-time constant eddy current are calculated, and the B0 eddy current and linear eddy current of the short-time constant eddy current can be accurately measured.

[0118] In an alternative embodiment, please refer to Figure 9 , Figure 9 This is a schematic diagram illustrating the direct terms of the short-time-constant eddy current B0 and the linear eddy current provided in an embodiment of this application. Figure 9 In this method, the test gradient G0, the layer selection gradient G1, and the layer selection back convergence gradient G2 are applied on the same gradient axis (applied to the X-axis, Y-axis, and Z-axis, respectively), which can measure the linear eddy current direct terms XX, YY, ZZ and the B0 eddy current XB0, YB0, ZB0. It should be noted that the test gradient G0 is applied after the layer selection gradient G1 and the layer selection back convergence gradient G2.

[0119] It is important to note that another difference between measuring the direct terms of B0 eddy current and linear eddy current for short-time constant eddy current and measuring the direct terms of B0 eddy current and linear eddy current for long-time constant eddy current is that measuring short-time constant eddy current does not require repetition; only one measurement of g is needed. r (t), through the formula

[0120] g r_short (t)=G0-g r (t)

[0121] Obtain the direct terms of the B0 term for short-time constant eddies and linear eddies; where the B0 term for the short-time eddies is g. r The constant term of (t).

[0122] In an alternative embodiment, please refer to Figure 10 , Figure 10 This is a schematic diagram illustrating the measurement of the cross term of a short-time-constant linear eddy current according to an embodiment of this application. G0 is applied after the layer selection gradient G1 and the layer selection retraction gradient G2. The test gradient G0 and the layer selection gradients G1 and G2 are applied on different gradient axes. For example, applying G0 to the X-axis and G1 / G2 to the Y-axis allows measurement of the linear eddy current cross term XY; applying G0 to the X-axis and G1 / G2 to the Z-axis allows measurement of the linear eddy current cross term XZ; applying G0 to the Y-axis and G1 / G2 to the X-axis allows measurement of the linear eddy current cross term YX; applying G0 to the Y-axis and G1 / G2 to the Z-axis allows measurement of the linear eddy current cross term YZ; applying G0 to the Z-axis and G1 / G2 to the X-axis allows measurement of the linear eddy current cross term ZX; and applying G0 to the Z-axis and G1 / G2 to the Y-axis allows measurement of the linear eddy current cross term ZY. The difference between the direct terms of B0 eddy current and linear eddy current, which are used to measure short-time constant eddy currents, lies in g. r (t) represents the short eddy current of the cross term.

[0123] Please see Figure 11 , Figure 11 This is a schematic diagram of alternating sampling provided in an embodiment of this application; the method includes: repeating the method after a certain time interval, thereby measuring the eddy current values ​​at different time points and improving the time accuracy of the measurement. Figure 11 As shown, the first measurement yields eddies at t1, t3, t5, and t7, while the second measurement, after a delay of d0, yields eddies at t2, t4, t6, and t8.

[0124] pass Figure 11 It can be seen that by repeating this method after a certain time interval, the eddy current values ​​at different time points can be measured, thus improving the time accuracy of the measurement. This overcomes the defect of the eddy current measurement method using multiple gradient echo (GRE) acquisition, where the eddy current value at each measurement time point is the average value over the echo time (TE), which cannot accurately reflect the magnitude of the eddy current at the sampling time.

[0125] Please check Figure 12 , Figure 12 This is a schematic diagram of the eddy current measurement device provided in an embodiment of this application; the eddy current measurement device 100 includes: a signal application module 110, a signal acquisition module 120 and an eddy current measurement module 130.

[0126] The signal application module 110 is used to apply a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection re-convergence gradient, and a de-phase gradient to a preset area of ​​the water model; wherein, the test gradient is used to generate eddy currents; the radio frequency pulse signal is used to generate magnetic resonance signals; the layer selection gradient is used to select the direction of the gradient magnetic field in the layer direction; the layer selection re-convergence gradient is used to re-converge the de-phase signal generated by the layer selection gradient; the de-phase gradient is used to de-phase the excited residual magnetization vector; and the water model is used to provide the magnetic resonance signal required for eddy current measurement.

[0127] The signal acquisition module 120 is used to acquire the magnetic resonance signal generated by the radio frequency pulse signal in the preset area.

[0128] Eddy current measurement module 130 is used to measure B0 eddy current and linear eddy current of long time constant and short time constant eddy current respectively based on magnetic resonance signal; wherein, B0 eddy current is eddy current independent of spatial position; linear eddy current is first-order eddy current in magnetic resonance signal that is spatially related; magnetic resonance signal includes magnetic resonance signal generated by radio frequency pulse signal in preset area.

[0129] In an optional embodiment, the test gradient includes a first test gradient and a second test gradient with opposite polarities; the magnetic resonance signal includes a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal. The signal application module 110 applies a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection re-convergence gradient, and a dispersion gradient to a preset area of ​​the water model, including: after applying the first test gradient to the preset area, the signal application module 110 applies the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient to the preset area of ​​the water model. After applying the second test gradient to the preset area, the signal application module 110 applies the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient to the preset area of ​​the water model. The process of acquiring magnetic resonance signals generated by radio frequency pulse signals in a preset region, and measuring the B0 eddy current and linear eddy current of long-time constant and short-time constant eddy currents based on the magnetic resonance signals, includes: a signal acquisition module 120 acquiring a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal in the preset region; wherein the first and second magnetic resonance signals include magnetic resonance signals corresponding to a first test gradient; and the third and fourth magnetic resonance signals include magnetic resonance signals corresponding to a second test gradient. An eddy current measurement module 130 calculates the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals.

[0130] In an optional embodiment, the layer selection gradient includes a first layer selection gradient and a second layer selection gradient with opposite polarities; the layer selection re-convergence gradient includes a first layer selection re-convergence gradient and a second layer selection re-convergence gradient with opposite polarities; the preset region includes a first preset region and a second preset region. After the signal application module 110 applies the first test gradient to the preset region, it applies a radio frequency pulse signal, a layer selection gradient, a layer selection re-convergence gradient, and a dispersive gradient to the preset region of the water model. This includes: after the signal application module 110 applies the test gradient to the first preset region, it applies a radio frequency pulse signal, a first layer selection gradient, a first layer selection re-convergence gradient, and a dispersive gradient to the first preset region of the water model, and acquires a first magnetic resonance signal in the first preset region; wherein, the test gradient is located on the same gradient axis as the first layer selection gradient and the first layer selection re-convergence gradient. After the signal application module 110 applies the first test gradient to the second preset region, it applies a radio frequency pulse signal, a second layer selection gradient, a second layer selection re-convergence gradient, and a dispersive gradient to the second preset region of the water model, and acquires a second magnetic resonance signal in the second preset region; wherein, the test gradient is located on the same gradient axis as the second layer selection gradient and the second layer selection re-convergence gradient. The calculation of the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals includes: signal acquisition module 120 acquiring the first, second, third, and fourth magnetic resonance signals; and eddy current measurement module 130 calculating the direct terms of the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals.

[0131] In an optional embodiment, after the signal application module 110 applies a first test gradient to a preset region, applying a radio frequency pulse signal, a layer selection gradient, a layer selection re-convergence gradient, and a dispersion gradient to the preset region of the water model further includes: after the signal application module 110 applies a test gradient to the first preset region, applying a radio frequency pulse signal, a first layer selection gradient, a first layer selection re-convergence gradient, and a dispersion gradient to the first preset region of the water model, and acquiring a first magnetic resonance signal of the first preset region; wherein the test gradient is located on a different gradient axis than the first layer selection gradient and the first layer selection re-convergence gradient. After the signal application module 110 applies a first test gradient to a second preset region, applying a radio frequency pulse signal, a second layer selection gradient, a second layer selection re-convergence gradient, and a dispersion gradient to the second preset region of the water model, and acquiring a second magnetic resonance signal of the second preset region; wherein the test gradient is located on a different gradient axis than the second layer selection gradient and the second layer selection re-convergence gradient. The calculation of the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals includes: acquiring the first, second, third, and fourth magnetic resonance signals; and the eddy current measurement module 130 calculating the cross term of the linear eddy current of the long-time constant eddy current based on the first, second, third, and fourth magnetic resonance signals.

[0132] In an optional embodiment, after the signal application module 110 applies a test gradient to a first preset region, it applies a radio frequency pulse signal, a first layer selection gradient, a first layer selection re-convergence gradient, and a dispersion gradient to the first preset region of the water model, and acquires a first magnetic resonance signal in the first preset region. This includes: after the signal application module 110 applies the first test gradient to a first gradient axis, it applies a radio frequency pulse signal, a first layer selection gradient, a first layer selection re-convergence gradient, and a dispersion gradient to a second gradient axis; wherein the first gradient axis and the second gradient axis are X gradient axes, Y gradient axes, or Z gradient axes, and the first gradient axis and the second gradient axis are not simultaneously the same gradient axis. The eddy current measurement module 130 calculates the cross term of the time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal. This includes: the eddy current measurement module 130 calculates the cross term of the first gradient axis and the second gradient axis of the time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal.

[0133] In an optional embodiment, after the eddy current measurement module 130 calculates the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal, the eddy current measurement method further includes: repeating the method after a certain time interval, so that the eddy current measurement module 130 can obtain the B0 eddy current and linear eddy current of the long-time constant eddy current at multiple different time points.

[0134] In an optional embodiment, the signal application module 110 applies a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection re-convergence gradient, and a dispersion gradient to a preset area of ​​the water model, including: after applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient, the signal application module 110 applies a first test gradient to the preset area of ​​the water model; after applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-convergence gradient, and the dispersion gradient, the signal application module 110 applies a second test gradient to the preset area of ​​the water model. The signal acquisition module 120 acquires the magnetic resonance signal generated by the radio frequency pulse signal in a preset area, and measures the B0 eddy current and linear eddy current of the long time constant and short time constant eddy currents respectively based on the magnetic resonance signal. This includes: the signal acquisition module 120 acquires a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal and a fourth magnetic resonance signal in the preset area; wherein, the first magnetic resonance signal and the second magnetic resonance signal include magnetic resonance signals corresponding to the first test gradient; the third magnetic resonance signal and the fourth magnetic resonance signal include magnetic resonance signals corresponding to the second test gradient; the eddy current measurement module 130 calculates the B0 eddy current and linear eddy current of the short time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

[0135] Please see Figure 13 , Figure 13 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. An electronic device 300 provided in this application includes: a processor 301 and a memory 302. The memory 302 stores machine-readable instructions executable by the processor 301. When the machine-readable instructions are executed by the processor 301, the method described above is performed.

[0136] Based on the same inventive concept, embodiments of this application also provide a computer-readable storage medium storing computer program instructions, which, when read and executed by a processor, perform the steps in any of the above implementations.

[0137] The computer-readable storage medium can be any medium capable of storing program code, such as Random Access Memory (RAM), Read Only Memory (ROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM). The storage medium stores the program, and the processor executes the program after receiving an execution instruction. The method executed by the electronic terminal as defined in any embodiment of this invention can be applied to the processor or implemented by the processor.

[0138] In the embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.

[0139] Furthermore, the units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0140] Furthermore, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0141] It can be replaced and can be implemented, wholly or partially, through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented, wholly or partially, in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated.

[0142] The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means.

[0143] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0144] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for measuring eddy currents, characterized in that, The method includes: Apply radio frequency pulse signals, test gradients, layer selection gradients, layer re-aggregation gradients, and dispersion gradients to a preset area of ​​the water model; The test gradient is used to generate eddy currents; the radio frequency pulse signal is used to generate magnetic resonance signals; the layer selection gradient is used to select the direction of the gradient magnetic field in the layer direction; the layer selection convergence gradient is used to converge the dephased signal generated by the layer selection gradient; the dispersion gradient is used to disperse the excited residual magnetization vector; and the water model is used to provide the magnetic resonance signal required for eddy current measurement. The radio frequency pulse signal generates a magnetic resonance signal in the preset area, and the B0 eddy current and linear eddy current of the long time constant eddy current and the short time constant eddy current are measured according to the magnetic resonance signal. Wherein, the B0 eddy current is an eddy current independent of spatial position; the linear eddy current is a first-order eddy current in the magnetic resonance signal that is spatially related; the magnetic resonance signal includes the magnetic resonance signal generated by the radio frequency pulse signal in the preset region; The test gradient includes a first test gradient and a second test gradient with opposite polarities; the magnetic resonance signal includes a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal. The application of radio frequency pulse signals, test gradients, layer selection gradients, layer selection re-aggregation gradients, and dispersion gradients to the preset area of ​​the water model includes: After applying the first test gradient to the preset region, the radio frequency pulse signal, the layer selection gradient, the layer selection re-aggregation gradient, and the dispersion gradient are applied to the preset region of the water model. After applying the second test gradient to the preset area, the radio frequency pulse signal, the layer selection gradient, the layer selection re-aggregation gradient, and the dispersion gradient are applied to the preset area of ​​the water model. The process of acquiring the magnetic resonance signal generated by the radio frequency pulse signal in the preset region, and measuring the B0 eddy current and linear eddy current of the long time constant and short time constant eddy currents respectively based on the magnetic resonance signal, includes: The first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal are acquired in the preset area; wherein, the first magnetic resonance signal and the second magnetic resonance signal include magnetic resonance signals corresponding to the first test gradient; the third magnetic resonance signal and the fourth magnetic resonance signal include magnetic resonance signals corresponding to the second test gradient; The B0 eddy current and linear eddy current of the long-time constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

2. The method according to claim 1, characterized in that, The layer selection gradient includes a first layer selection gradient and a second layer selection gradient with opposite polarities; the layer selection re-convergence gradient includes a first layer selection re-convergence gradient and a second layer selection re-convergence gradient with opposite polarities; the preset region includes a first preset region and a second preset region; After applying the first test gradient to the preset region, applying the radio frequency pulse signal, the layer selection gradient, the layer selection reconvergence gradient, and the dispersion gradient to the preset region of the water model includes: After applying the first test gradient to the first preset region, the radio frequency pulse signal, the first layer selection gradient, the first layer selection re-convergence gradient, and the dispersion gradient are applied to the first preset region of the water model; wherein, the test gradient is located on the same gradient axis as the first layer selection gradient and the first layer selection re-convergence gradient; After applying the first test gradient to the second preset region, the radio frequency pulse signal, the second layer selection gradient, the second layer selection re-convergence gradient, and the dispersion gradient are applied to the second preset region of the water model; wherein, the test gradient, the second layer selection gradient, and the second layer selection re-convergence gradient are located on the same gradient axis; The calculation of the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal includes: The first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal are acquired. The B0 eddy current and the direct term of the linear eddy current of the long-time constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal.

3. The method according to claim 2, characterized in that, After applying the first test gradient to the preset region, applying the radio frequency pulse signal, the layer selection gradient, the layer selection reconvergence gradient, and the dispersion gradient to the preset region of the water model further includes: After applying the test gradient to the first preset region, the radio frequency pulse signal, the first layer selection gradient, the first layer selection re-convergence gradient, and the dispersion gradient are applied to the first preset region of the water model, and the first magnetic resonance signal of the first preset region is acquired; wherein, the test gradient is located on a different gradient axis from the first layer selection gradient and the first layer selection re-convergence gradient; After applying the first test gradient to the second preset region, the radio frequency pulse signal, the second layer selection gradient, the second layer selection re-convergence gradient, and the dispersion gradient are applied to the second preset region of the water model, and the second magnetic resonance signal of the second preset region is obtained; wherein, the test gradient is located on a different gradient axis from the second layer selection gradient and the second layer selection re-convergence gradient; The step of calculating the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal includes: The first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal are acquired. The cross term of the linear eddy current of the long-time constant eddy current is calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal.

4. The method according to claim 3, characterized in that, After applying the test gradient to the first preset region, the radio frequency pulse signal, the first layer selection gradient, the first layer selection re-convergence gradient, and the dispersive gradient are applied to the first preset region of the water model, and the first magnetic resonance signal of the first preset region is acquired; wherein, the test gradient is located on a different gradient axis from the first layer selection gradient and the first layer selection re-convergence gradient, including: After applying the first test gradient to the first gradient axis, the radio frequency pulse signal, the first layer selection gradient, the first layer selection regrouping gradient, and the breakup gradient are applied to the second gradient axis; wherein, the first gradient axis and the second gradient axis are X gradient axis, Y gradient axis, or Z gradient axis, and the first gradient axis and the second gradient axis are not the same gradient axis at the same time; The calculation of the cross term of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal includes: The first gradient axis and second gradient axis intersection term of the time constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal.

5. The method according to claim 1, characterized in that, After calculating the B0 eddy current and linear eddy current of the long-time constant eddy current based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal, the method further includes: After a certain time interval, the method is repeated to obtain the B0 eddy and the linear eddy of the long-time constant eddy at multiple different time points.

6. The method according to claim 1, characterized in that, The application of radio frequency pulse signals, test gradients, layer selection gradients, layer selection re-aggregation gradients, and dispersion gradients to the preset area of ​​the water model includes: After applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-aggregation gradient, and the dispersion gradient, the first test gradient is applied to the preset area to the preset area of ​​the water model; After applying the radio frequency pulse signal, the layer selection gradient, the layer selection re-aggregation gradient, and the dispersion gradient, the second test gradient is applied to the preset area to the preset area of ​​the water model; The process of acquiring the magnetic resonance signal generated by the radio frequency pulse signal in the preset region, and measuring the B0 eddy current and linear eddy current of the long time constant and short time constant eddy currents respectively based on the magnetic resonance signal, includes: The first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal are acquired in the preset area; wherein, the first magnetic resonance signal and the second magnetic resonance signal include magnetic resonance signals corresponding to the first test gradient; the third magnetic resonance signal and the fourth magnetic resonance signal include magnetic resonance signals corresponding to the second test gradient; The B0 eddy current and linear eddy current of the short time constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

7. An eddy current measuring device, characterized in that, The eddy current measurement device includes: a signal application module, a signal acquisition module, and an eddy current measurement module; The signal application module is used to apply a radio frequency pulse signal, a test gradient, a layer selection gradient, a layer selection refocusing gradient, and a dispersion gradient to a preset area of ​​the water model; wherein, the test gradient is used to generate eddy currents; the radio frequency pulse signal is used to generate a magnetic resonance signal; the layer selection gradient is used to select the direction of the gradient magnetic field in the layer direction; the layer selection refocusing gradient is used to refocus the dephasing signal generated by the layer selection gradient; the dispersion gradient is used to disperse the excited residual magnetization vector; and the water model is used to provide the magnetic resonance signal required for eddy current measurement. The signal acquisition module is used to acquire the magnetic resonance signal generated by the radio frequency pulse signal in the preset area; The eddy current measurement module is used to measure the B0 eddy current and linear eddy current of long-time constant and short-time constant eddy currents respectively based on the magnetic resonance signal; wherein, the B0 eddy current is an eddy current independent of spatial position; the linear eddy current is a first-order eddy current in the magnetic resonance signal that is spatially related; the magnetic resonance signal includes the magnetic resonance signal generated by the radio frequency pulse signal in the preset region; The test gradient includes a first test gradient and a second test gradient with opposite polarities; the magnetic resonance signal includes a first magnetic resonance signal, a second magnetic resonance signal, a third magnetic resonance signal, and a fourth magnetic resonance signal. The signal application module is specifically used for: After applying the first test gradient to the preset region, the radio frequency pulse signal, the layer selection gradient, the layer selection re-aggregation gradient, and the dispersion gradient are applied to the preset region of the water model. After applying the second test gradient to the preset area, the radio frequency pulse signal, the layer selection gradient, the layer selection re-aggregation gradient, and the dispersion gradient are applied to the preset area of ​​the water model. The signal acquisition module is specifically used for: The first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal, and the fourth magnetic resonance signal are acquired in the preset area; wherein, the first magnetic resonance signal and the second magnetic resonance signal include magnetic resonance signals corresponding to the first test gradient; the third magnetic resonance signal and the fourth magnetic resonance signal include magnetic resonance signals corresponding to the second test gradient; The B0 eddy current and linear eddy current of the long-time constant eddy current are calculated based on the first magnetic resonance signal, the second magnetic resonance signal, the third magnetic resonance signal and the fourth magnetic resonance signal.

8. An electronic device, characterized in that, The electronic device includes a memory and a processor. The memory stores program instructions, and when the processor executes the program instructions, it performs the steps of the method according to any one of claims 1-6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer program instructions that, when executed by a processor, perform the steps of the method according to any one of claims 1-6.

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