Radio frequency transmit field detection method, apparatus, magnetic resonance system, and storage medium

Abstract

The application relates to a radio frequency transmit field detection method and device, a radio frequency transmit field correction method, a magnetic resonance system, a storage medium and a computer program product. The method comprises: acquiring at least two groups of magnetic resonance echo signals. Each group of magnetic resonance echo signals is generated by exciting a detection object by a radio frequency transmit pulse with a different preset flip angle, and the different preset flip angles conform to a predetermined relationship. According to each group of magnetic resonance echo signals, a flip angle probability density distribution function corresponding to a radio frequency transmit field is determined. The flip angle probability density distribution function represents the probability density distribution of the flip angle of the radio frequency transmit field in the case that a characteristic quantity of the magnetic resonance echo signal is at a set value. According to the flip angle probability density distribution function and the magnetic resonance echo signal, the distribution of the radio frequency transmit field is determined. By using the method, the actual offset of the radio frequency transmit field is detected to determine the uniformity of the radio frequency transmit field.

Description

Technical Field

[0001] This application relates to the field of magnetic resonance imaging technology, and in particular to a radio frequency emission field detection method, apparatus, radio frequency emission field correction method, magnetic resonance system, storage medium and computer program product. Background Technology

[0002] Non-uniformity of the radio frequency (RF) emission field in a magnetic resonance imaging (MRI) system can negatively impact the quality of MRI images. Therefore, it is necessary to measure the uniformity of the RF emission field. If non-uniformity is detected, the negative impact caused by this non-uniformity can be effectively assessed and corrected as much as possible.

[0003] Current methods for detecting radio frequency (RF) emission fields involve collecting magnetization vectors reflected from human tissue (also known as magnetic resonance echo signals), determining the signal flip angle, and then using the signal flip angle to determine the RF emission field intensity, thereby detecting the uniformity of the RF emission field.

[0004] However, current methods for detecting radio frequency (RF) emission fields have limitations in terms of angle range. When the RF emission field is non-uniform, the actual signal flip angle may be too large or too small. If the actual signal flip angle exceeds the range of angles that can be solved using current methods, the signal flip angle cannot be calculated, and therefore the intensity of the RF emission field cannot be determined. Therefore, there is an urgent need for a method for detecting the intensity of RF emission fields. Summary of the Invention

[0005] Therefore, it is necessary to provide a radio frequency emission field detection method, apparatus, radio frequency emission field correction method, magnetic resonance system, computer-readable storage medium, and computer program product to address the above-mentioned technical problems.

[0006] Firstly, this application provides a method for detecting radio frequency emission fields. The method includes:

[0007] Acquire at least two magnetic resonance echo signal groups and determine the target signal ratio for each magnetic resonance echo signal group;

[0008] Based on the joint probability density distribution function corresponding to the magnetic resonance echo signal group and the preset probability algorithm, a flip angle probability density distribution function is constructed; the flip angle probability density distribution function characterizes the distribution of the radio frequency transmission field offset under the condition that the signal ratio is constant.

[0009] Given that the signal ratio in the flip angle probability density distribution function is the target signal ratio, the actual offset of the radio frequency transmission field is determined based on the flip angle probability density distribution function.

[0010] In one embodiment, determining the flip angle probability density distribution function corresponding to the radio frequency transmission field based on each set of magnetic resonance echo signals includes:

[0011] Obtain the joint probability density distribution function corresponding to the magnetic resonance echo signal;

[0012] Based on the joint probability density distribution function and the preset probability algorithm, a flip angle probability density distribution function is constructed.

[0013] In one embodiment, obtaining the joint probability density distribution function corresponding to the magnetic resonance echo signal includes:

[0014] Obtain the distribution function corresponding to the magnetic resonance echo signal, and perform a ratio calculation on the distribution function corresponding to the magnetic resonance echo signal in each group to determine the probability density distribution function corresponding to each group of magnetic resonance echo signals;

[0015] A joint probability density distribution function is constructed based on the probability density distribution functions corresponding to at least two sets of magnetic resonance echo signals.

[0016] In one embodiment, constructing the flip angle probability density distribution function based on the joint probability density distribution function and the preset probability algorithm includes:

[0017] By integrating the offset of the radio frequency transmission field contained in the joint probability density distribution function, the total probability density distribution function corresponding to the magnetic resonance echo signal within a preset range of the offset is obtained.

[0018] The flip angle probability density distribution function is constructed by calculating the ratio between the joint probability density distribution function and the total probability density distribution function.

[0019] Secondly, this application also provides a radio frequency transmission field correction method, the method comprising:

[0020] The detection object is excited by a scanning sequence, wherein the scanning sequence includes at least two sets of radio frequency emission pulse combinations, and the preset flip angles corresponding to the radio frequency emission pulse combinations conform to a predetermined relationship;

[0021] At least two sets of magnetic resonance echo signals are acquired, and each set of magnetic resonance echo signals corresponds to a set of radio frequency transmission pulse combinations.

[0022] Based on each set of magnetic resonance echo signals, the flip angle probability density distribution function corresponding to the radio frequency transmission field is determined; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set;

[0023] The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal; and,

[0024] The parameters of the scanning sequence are adjusted according to the distribution of the radio frequency transmission field to obtain the target transmission field.

[0025] In one embodiment, the preset flip angles contained in the same group of radio frequency transmit pulse combinations conform to a linear relationship.

[0026] In one embodiment, the magnetic resonance echo signal includes a stimulated echo signal and a free-induction fading signal, and the characteristic quantity of the magnetic resonance echo signal is the ratio of the stimulated echo signal to the free-induction fading signal.

[0027] Thirdly, this application also provides a radio frequency emission field detection device. The device includes:

[0028] The acquisition module is used to acquire at least two sets of magnetic resonance echo signals; each set of magnetic resonance echo signals is generated by exciting the detection object with radio frequency transmission pulses of different preset flip angles, and the different preset flip angles conform to a predetermined relationship.

[0029] A construction module is used to determine the flip angle probability density distribution function corresponding to the radio frequency transmission field based on each group of magnetic resonance echo signals; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set;

[0030] The determination module is used to determine the distribution of the radio frequency transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0031] Fourthly, a magnetic resonance system is provided, comprising:

[0032] A main magnet, used to generate a main magnetic field, forms a scanning cavity;

[0033] A transmitting coil is disposed within the scanning cavity and has multiple transmitting channels, each of which is capable of generating a radio frequency transmitting pulse;

[0034] A receiving coil is used to acquire magnetic resonance echo signals after the radio frequency transmission pulse excites the detection object;

[0035] The processor, connected to the transmitting coil and the receiving coil respectively, is used to control the transmitting coil to transmit at least two sets of radio frequency (RF) transmission pulse combinations to the detection object, wherein the preset flip angles contained in the same set of RF transmission pulse combinations conform to a predetermined relationship; it is used to control the receiving coil to acquire at least two sets of magnetic resonance echo signals, each set of magnetic resonance echo signals corresponding to a set of RF transmission pulse combinations; it is used to determine the flip angle probability density distribution function corresponding to the RF transmission field based on each set of magnetic resonance echo signals; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the RF transmission field under a set value for the characteristic quantity of the magnetic resonance echo signal; and it determines the distribution of the RF transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signals.

[0036] In one embodiment, the processor is further configured to generate adjustment parameters for a scanning sequence based on the distribution of the radio frequency transmission field, the adjustment parameters of the scanning sequence being executable by the transmission coil to obtain the target transmission field.

[0037] Fifthly, this application also provides a computer device. The computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to perform the following steps:

[0038] At least two sets of magnetic resonance echo signals are acquired; each set of magnetic resonance echo signals is generated by exciting the detection object with radio frequency transmission pulses of different preset flip angles, and the different preset flip angles conform to a predetermined relationship.

[0039] Based on each set of magnetic resonance echo signals, the flip angle probability density distribution function corresponding to the radio frequency transmission field is determined; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set;

[0040] The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0041] Sixthly, this application also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program thereon, which, when executed by a processor, performs the following steps:

[0042] At least two sets of magnetic resonance echo signals are acquired; each set of magnetic resonance echo signals is generated by exciting the detection object with radio frequency transmission pulses of different preset flip angles, and the different preset flip angles conform to a predetermined relationship.

[0043] Based on each set of magnetic resonance echo signals, the flip angle probability density distribution function corresponding to the radio frequency transmission field is determined; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set;

[0044] The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0045] Seventhly, this application also provides a computer program product. The computer program product includes a computer program that, when executed by a processor, performs the following steps:

[0046] At least two sets of magnetic resonance echo signals are acquired; each set of magnetic resonance echo signals is generated by exciting the detection object with radio frequency transmission pulses of different preset flip angles, and the different preset flip angles conform to a predetermined relationship.

[0047] Based on each set of magnetic resonance echo signals, the flip angle probability density distribution function corresponding to the radio frequency transmission field is determined; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set;

[0048] The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0049] The aforementioned radio frequency (RF) transmitter field correction method, detection method, apparatus, RF transmitter field correction method, magnetic resonance system, storage medium, and computer program product include a computer device that acquires at least two sets of magnetic resonance echo signals. Each set of magnetic resonance echo signals is generated by RF transmission pulses with different preset flip angles exciting the detection object, and the different preset flip angles conform to a predetermined relationship. Based on each set of magnetic resonance echo signals, a flip angle probability density distribution function corresponding to the RF transmitter field is determined. The flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the RF transmitter field under a set value for the characteristic quantity of the magnetic resonance echo signal. Based on the flip angle probability density distribution function and the magnetic resonance echo signals, the distribution of the RF transmitter field is determined. Using this method, by constructing a flip angle probability density distribution function, the possible flip angle distribution of the radio frequency transmission field is obtained when the characteristic quantity of the magnetic resonance echo signal is set. Based on the target signal ratio determined by actual acquisition, the probability of the possible flip angle of the radio frequency transmission field when the target signal ratio appears in the radio frequency signal field is obtained. Then, the flip angle with the highest probability is taken as the actual flip angle of the radio frequency transmission field to verify the uniformity of the radio frequency transmission field. Attached Figure Description

[0050] Figure 1 This is a flowchart illustrating a radio frequency emission field detection method in one embodiment;

[0051] Figure 2 This is a flowchart illustrating the steps for constructing the flip angle probability density distribution function in one embodiment;

[0052] Figure 3 This is a flowchart illustrating the steps for constructing the joint probability density distribution function in one embodiment;

[0053] Figure 4 This is a flowchart illustrating the steps of constructing the flip angle probability density distribution function in one embodiment;

[0054] Figure 5 This is a flowchart illustrating the compensation steps using a noise distribution function in one embodiment.

[0055] Figure 6 This is a schematic diagram of the noise distribution function in one embodiment;

[0056] Figure 7 This is a schematic diagram of the intensity distribution function of the first magnetic resonance echo signal in one embodiment;

[0057] Figure 8 This is a schematic diagram of the intensity distribution function of the second magnetic resonance echo signal in one embodiment;

[0058] Figure 9 This is a schematic diagram of the probability density distribution function of the compensated signal ratio in one embodiment;

[0059] Figure 10 This is a flowchart illustrating a radio frequency transmit field correction method in one embodiment;

[0060] Figure 11 This is a structural block diagram of a radio frequency emission field detection device in one embodiment;

[0061] Figure 12 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0063] Magnetic Resonance Imaging (MRI) systems are widely used in the medical field. For example, MRI can be used to obtain images of human tissues, assisting doctors in disease diagnosis and medical research. The radio frequency (RF) system (or RF emission field) in MRI plays a crucial role. The RF system emits RF pulses under the excitation of a RF emission voltage. Under the influence of these pulses, the macroscopic magnetization vector of human tissues deviates from its equilibrium state; the angle of this deviation is called the flip angle. MRI then uses the acquired magnetization vectors to image the human tissues. During the imaging process, to prevent the magnetization vector excited by the RF emission field from negatively impacting the quality of the MRI image—that is, to ensure that the RF pulses reflected from the RF emission field achieve the expected flip angle—this application requires detecting whether the RF emission field is uniform. In practice, if the RF emission field is uniform, the desired flip angle can be obtained; if the RF emission field is non-uniform, it is necessary to further determine the negative impact caused by the non-uniformity and make corrections.

[0064] In one embodiment, such as Figure 1 As shown, a method for detecting radio frequency emission fields is provided. This embodiment illustrates the application of this method to a terminal. It is understood that this method can also be applied to a server, and further to a system including both a terminal and a server, and implemented through interaction between the terminal and the server. In this embodiment, the method includes the following steps:

[0065] Step 102: Acquire at least two sets of magnetic resonance echo signals.

[0066] Each set of magnetic resonance echo signals is generated by the detection object excited by radio frequency transmission pulses with different preset flip angles, and the different preset flip angles conform to a predetermined relationship.

[0067] In practice, the computer equipment controls the radio frequency (RF) transmission voltage by scanning a preset RF echo sequence (also known as a scan sequence), thereby exciting the RF system to emit RF pulses under the RF transmission voltage. This causes a shift in the macroscopic magnetization vector of the imaging object (also known as the detection object, such as human tissue) under the influence of the RF pulses. The computer equipment then acquires at least two sets of magnetic resonance echo signals of the imaging object under the magnetization vector shift state, with the preset flip angles corresponding to the same set of magnetic resonance echo signals conforming to a predetermined relationship. For each set of magnetic resonance echo signals, the target signal ratio of the two RF signals contained within it is calculated.

[0068] The scanning radio frequency echo sequence generates a set of magnetic resonance echo signals. Each set of magnetic resonance echo signals contains two different types of magnetic resonance echo signals, and each set of magnetic resonance echo signals corresponds to a flip angle (expected flip angle). Different preset flip angles conform to a predetermined relationship, which can be a linear relationship. For example, if the flip angle corresponding to the first set of magnetic resonance echo signals is α1, and α1 = α, then the flip angles corresponding to the subsequent second, third, and Nth sets of magnetic resonance echo signals can be: α2 = K2α, α3 = K3α…α N =K N α.

[0069] Optionally, the number of magnetic resonance echo signal groups acquired is not limited in this embodiment. If expressed in terms of the expected flip angle, this application can pre-acquire α1, α2, ... α n The magnetic resonance echo signal group corresponding to each flip angle.

[0070] Step 104: Determine the flip angle probability density distribution function corresponding to the radio frequency transmission field based on each set of magnetic resonance echo signals.

[0071] The flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under a set value for the characteristic quantity of the magnetic resonance echo signal.

[0072] In implementation, the computer device pre-stores multiple joint probability density distribution functions. Then, the computer device obtains the corresponding joint probability density distribution function based on the number of acquired magnetic resonance echo signal groups. Next, the computer device constructs a flip angle probability density distribution function based on this joint probability density distribution function and a preset probability algorithm. Specifically, the process of constructing the flip angle probability density distribution function will be described in detail in subsequent embodiments and will not be repeated here.

[0073] Optionally, when two sets of magnetic resonance echo signals are acquired, each set of magnetic resonance echo signals corresponds to a target signal ratio (also known as a characteristic quantity of the magnetic resonance echo signal). The resulting joint probability density function is then a joint probability density distribution function that simultaneously satisfies the conditions for two target signal ratios. Similarly, when three sets of magnetic resonance echo signals are acquired, each set of magnetic resonance echo signals corresponds to a target signal ratio. The resulting joint probability density function is then a joint probability density distribution function that simultaneously satisfies the conditions for three target signal ratios. This application does not limit the form of the joint probability density function in its embodiments.

[0074] Step 106: Determine the distribution of the radio frequency transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0075] In practice, the computer equipment uses the acquired magnetic resonance echo signals to calculate the signal ratio (also known as the target signal ratio, or a characteristic quantity of the magnetic resonance echo signal) between the two magnetic resonance echo signals in each group. This signal ratio is used as a known condition for solving the current RF transmission field flip angle. Substituting this ratio into the constructed flip angle probability density distribution function, the actual flip angle of the RF transmission field is determined. Furthermore, the computer equipment can determine the distribution of the RF transmission field based on the actual flip angle.

[0076] In a practical calculation example, regarding the signal ratio condition in the flip angle probability density distribution function, under the condition that the signal ratio condition is the target signal ratio, the computer device calculates the maximum possible value of the flip angle based on the constructed flip angle probability density distribution function, and uses this value as the actual flip angle of the RF transmission field. Furthermore, when scanning the RF echo sequence, each set of RF echo sequences corresponds to an expected flip angle of the RF transmission field. The difference between the expected flip angle and the actual flip angle can characterize the uniformity of the current RF transmission field. Optionally, the uniformity of the RF transmission field can characterize the distribution of the RF transmission field.

[0077] In the aforementioned radio frequency (RF) transmission field detection method, a computer device acquires at least two sets of magnetic resonance echo signals. Then, based on each set of magnetic resonance echo signals, the computer device determines the flip angle probability density distribution function corresponding to the RF transmission field. This flip angle probability density distribution function characterizes the probability density distribution of the RF transmission field's flip angle when the characteristic quantities of the magnetic resonance echo signals are set to a certain value. Then, the computer device determines the distribution of the RF transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signals. Using this method, by constructing the flip angle probability density distribution function, the possible distribution of flip angles in the RF transmission field when the characteristic quantities of the magnetic resonance echo signals are set to a certain value is obtained. Based on the target signal ratio determined by actual acquisition, the probability of the possible flip angle corresponding to the target signal ratio appearing in the RF signal field is obtained. Finally, the flip angle with the highest probability is taken as the actual flip angle of the RF transmission field to verify the uniformity of the RF transmission field.

[0078] In one embodiment, such as Figure 2 As shown, the specific processing steps of step 102 include the following steps:

[0079] Step 202: Obtain the joint probability density distribution function corresponding to the magnetic resonance echo signal.

[0080] In implementation, the computer equipment obtains the joint probability density distribution function corresponding to the acquired magnetic resonance echo signal group. For example, the computer equipment acquires two magnetic resonance echo signal groups, each of which may include free induction decay (FID) and stimulated echo (STE) signals. In this embodiment, these two magnetic resonance echo signal groups are designated as the first magnetic resonance echo signal group: and The first STE signal, The first FID signal; and the second magnetic resonance echo signal group: and This is the second STE signal. This is the second FID signal. The target signal ratio for these two sets of magnetic resonance echo signals can be denoted as: and Furthermore, the joint probability density distribution function corresponding to these two magnetic resonance echo signal groups is determined as follows:

[0081]

[0082] Where P represents the offset of the radio frequency (RF) transmission field, α1 represents the expected flip angle corresponding to the first magnetic resonance echo signal group, α2 represents the expected flip angle corresponding to the second magnetic resonance echo signal group, Pα1 represents the actual flip angle under the excitation of the first magnetic resonance echo signal group, and Pα2 represents the actual flip angle under the excitation of the second magnetic resonance echo signal group. This joint probability density distribution function characterizes the distribution of the signal ratios corresponding to the magnetic resonance echo signal groups under the condition that the offset of the RF transmission field is constant (i.e., the actual flip angle corresponding to the RF transmission field is constant).

[0083] Step 204: Construct the flip angle probability density distribution function based on the joint probability density distribution function and the preset probability algorithm.

[0084] In implementation, the computer equipment constructs the flip angle density distribution function based on the joint probability density distribution function and the preset probability algorithm.

[0085] In one embodiment, such as Figure 3 As shown, the specific processing steps of step 202 include the following steps:

[0086] Step 302: Obtain the distribution function corresponding to the magnetic resonance echo signal, and perform a ratio calculation on the distribution function corresponding to the magnetic resonance echo signal in each group to determine the probability density distribution function corresponding to each group of magnetic resonance echo signals.

[0087] Among them, the magnetic resonance echo signal corresponds to the magnetic resonance echo signal distribution function.

[0088] In practice, the computer equipment acquires the magnetic resonance echo signal distribution function (MREC) contained in each set of MREC signals. For example, given two sets of MREC signals: the first set of MREC signals contains... and The second set of magnetic resonance echo signals includes and The distribution function of the intensity of each magnetic resonance echo signal is shown below:

[0089]

[0090]

[0091]

[0092]

[0093] In the above distribution function, M1 and M2 are the longitudinal magnetization vectors of the radio frequency transmission field, α1 and α2 are the flip angles in the radio frequency transmission field, and β is the reference flip angle.

[0094] Then, the computer equipment performs a ratio calculation on the distribution functions of the magnetic resonance echo signals in the magnetic resonance echo signal group to determine the probability density distribution function corresponding to the signal ratio of the magnetic resonance echo signal group.

[0095] Specifically, taking the probability density distribution function of the first magnetic resonance echo signal group as an example, the formula for calculating the probability density distribution function of the first magnetic resonance echo signal group is as follows:

[0096]

[0097] Similarly, the calculation formula for the probability density distribution function of the second magnetic resonance echo signal group is the same as that of the first magnetic resonance echo signal group, and will not be repeated in the embodiments of this application.

[0098] Step 304: Construct a joint probability density distribution function based on the probability density distribution functions corresponding to at least two sets of magnetic resonance echo signals.

[0099] In implementation, the computer device constructs a joint probability density distribution function based on the probability density distribution functions of at least two magnetic resonance echo signal groups. In one embodiment, the computer device constructs a joint probability density distribution function using the probability density distribution functions of the first and second magnetic resonance echo signal groups.

[0100] In one embodiment, such as Figure 4As shown, the specific processing steps of step 202 include the following steps:

[0101] Step 402: Integrate the offset of the radio frequency transmission field contained in the joint probability density distribution function to obtain the total probability density distribution function corresponding to the magnetic resonance echo signal within the preset range of the offset.

[0102] In practice, the computer equipment performs an integral operation on the offset of the radio frequency transmission field contained in the joint probability density distribution function within a preset offset range to obtain the full probability density distribution function of the magnetic resonance echo signal ratio within the preset offset range.

[0103] Specifically, the formula for the total probability density function is shown below:

[0104]

[0105] Among them, P max This represents the preset maximum offset value. The full probability density distribution function characterizes the signal ratio distribution under the condition that the offset takes any fixed value point within the preset range.

[0106] Step 404: Calculate the ratio of the joint probability density distribution function and the total probability density distribution function to construct the flip angle probability density distribution function.

[0107] In implementation, the computer equipment calculates the ratio of the joint probability density function and the total probability density function to determine the probability of the offset condition (i.e., the condition that the offset takes a certain value) within the range of all offset values ​​corresponding to the joint probability density function. Since there is a correspondence between the offset P and the actual flip angle, for example, the actual flip angle α1 = Pα, where α is the expected flip angle, substituting these values ​​into the formula for the flip angle yields the flip angle probability density function. Specifically, the formula for calculating the flip angle probability density function is as follows:

[0108]

[0109] In this embodiment, the total probability density distribution function is calculated by using the joint probability density distribution function, and then the flip angle probability density distribution function is constructed using the joint probability density distribution function and the total probability density distribution function. The flip angle of the radio frequency transmission field is calculated in this way, realizing a method to determine the offset of the radio frequency transmission field in a probabilistic form. By simulating all flip angles of the radio frequency transmission field in a probabilistic form, the distribution of all possible flip angles is obtained, and then the flip angle corresponding to the target signal ratio is determined.

[0110] In one embodiment, such as Figure 5As shown, for the probability density distribution function of the magnetic resonance echo signal constructed in the above embodiments, the noise influence of the radio frequency transmission field itself needs to be further considered, that is, the difference between the flip angle of the radio frequency transmission field and the expected flip angle caused by the non-radio frequency transmission field inhomogeneity. Therefore, based on the existing joint probability density distribution function, noise compensation is required. The specific processing procedure for obtaining the distribution function corresponding to the magnetic resonance echo signal in step 302 includes:

[0111] Step 502: Obtain the preset noise distribution function.

[0112] In implementation, the computer equipment acquires a preset noise distribution function for the radio frequency transmission field. Among these, noise (I0) n The distribution satisfies the normal distribution function, such as Figure 6 As shown, specifically, the distribution function of the noise distribution is as follows, where σ represents the standard deviation:

[0113]

[0114] Step 504: Compensate the initial distribution function of the magnetic resonance echo signal according to the noise distribution function to obtain the distribution function of each magnetic resonance echo signal.

[0115] In practice, the computer equipment compensates for the initial distribution function of the magnetic resonance echo signal based on the noise distribution function. That is, it compensates for the error in the initial distribution function that does not consider the influence of radio frequency transmission field noise by adding the two functions together, and obtains the distribution function of each magnetic resonance echo signal after compensation.

[0116] Specifically, let's take two echo signals from the first magnetic resonance echo signal group as an example, such as... Figure 7 As shown, the compensated signal intensity distribution function of the first magnetic resonance echo signal (referred to as the first signal) contained in the first magnetic resonance echo signal group is as follows: like Figure 8 As shown, the compensated distribution function of the second magnetic resonance echo signal (referred to as the second signal) included in the first magnetic resonance echo signal group is:

[0117] Optional, such as Figure 9 As shown, based on the distribution function of each compensated magnetic resonance echo signal, the compensated probability density distribution function of the magnetic resonance echo signal is specifically determined as follows:

[0118]

[0119] Furthermore, based on the compensated probability density distribution function, a flip angle probability density distribution function can be constructed to improve the accuracy of the flip angle.

[0120] In one embodiment, such as Figure 10 As shown, a radio frequency transmit field correction method is provided, the method comprising:

[0121] Step 1001: Excite the detection target using the scanning sequence.

[0122] The scanning sequence includes at least two sets of radio frequency transmission pulse combinations, and the preset flip angle corresponding to the radio frequency transmission pulse combination conforms to a predetermined relationship. For example, the preset flip angle of the same set of radio frequency transmission pulse combinations conforms to a linear relationship.

[0123] In practice, the computer equipment emits a combination of pulses according to a preset scanning sequence, which excites the target object.

[0124] Step 1002: Acquire at least two sets of magnetic resonance echo signals.

[0125] Each set of magnetic resonance echo signals corresponds to a set of radio frequency transmission pulse combinations.

[0126] In practice, the computer equipment acquires at least two sets of magnetic resonance echo signals. For example, each set of magnetic resonance echo signals includes a first echo signal and a second echo signal.

[0127] Optionally, the first signal included in each group of magnetic resonance echo signals may be, but is not limited to, I. STE (Excitation echo signal), the second signal may be, but is not limited to, I. FID (Free-induction decay signal), the computer equipment collects two sets of magnetic resonance echo signals, which are respectively and and

[0128] Step 1003: Determine the flip angle probability density distribution function corresponding to the radio frequency transmission field based on each group of magnetic resonance echo signals.

[0129] The flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under a set value for the characteristic quantity of the magnetic resonance echo signal.

[0130] In implementation, the computer equipment obtains the corresponding joint probability density distribution function and a preset probability density algorithm based on the number of acquired magnetic resonance echo signal groups, and constructs the flip angle probability density distribution function. This process has been described in detail in steps 402 to 404 above, and will not be repeated here.

[0131] Step 1004: Determine the distribution of the radio frequency transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0132] In practice, assuming the flip angle probability density distribution function has already been constructed,

[0133] The computer equipment calculates the signal ratio of the magnetic resonance echo signal within each group. Then, using this signal ratio as a known condition for solving the current RF transmission field flip angle, it substitutes it into the constructed flip angle probability density distribution function to determine the actual flip angle of the RF transmission field. Furthermore, the computer equipment can determine the distribution of the RF transmission field based on the actual flip angle.

[0134] The specific process for determining the flip angle of the current RF transmission field is as follows: The computer equipment calculates the maximum value of the flip angle probability density distribution function under the condition that the signal ratio is equal to the target signal ratio. This maximum value represents the highest probability of the flip angle occurring among various possible values ​​given the target signal ratio. Since the flip angle corresponding to the maximum value of the flip angle probability density distribution function represents the most likely flip angle value among all possible flip angle values ​​under the condition that the signal ratio is equal to the target signal ratio, the computer equipment uses this flip angle value as the actual flip angle of the RF transmission field and uses it as the standard for detecting the uniformity of the RF transmission field.

[0135] Step 1005: Adjust the parameters of the scanning sequence according to the distribution of the radio frequency transmission field to obtain the target transmission field.

[0136] In practice, the computer equipment adjusts the parameters of the scanning sequence in reverse according to the distribution of the radio frequency transmission field to obtain the target transmission field. This target transmission field is a uniformly distributed radio frequency transmission field.

[0137] In one embodiment, the magnetic resonance echo signal includes a stimulated echo (STE) signal and a free induction fading (FID) signal, and the characteristic quantity of the magnetic resonance echo signal is the ratio of the stimulated echo signal to the free induction fading signal.

[0138] In one embodiment, the magnetic resonance echo signal includes a stimulated echo signal and a free-induction fading signal, and the characteristic quantity of the magnetic resonance echo signal is the ratio of the stimulated echo signal to the free-induction fading signal.

[0139] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0140] Based on the same inventive concept, this application also provides an RF emission field detection apparatus for implementing the RF emission field detection method described above. The solution provided by this apparatus is similar to the implementation described in the above method; therefore, the specific limitations in one or more RF emission field detection apparatus embodiments provided below can be found in the limitations of the RF emission field detection method described above, and will not be repeated here.

[0141] In one embodiment, such as Figure 11 As shown, a radio frequency emission field detection device 1100 is provided, including: an acquisition module, a construction module, and a determination module, wherein:

[0142] Acquisition module 1101 is used to acquire at least two magnetic resonance echo signal groups; each group of magnetic resonance echo signals is generated by radio frequency transmission pulses with different preset flip angles exciting the detection object, and the different preset flip angles conform to a predetermined relationship.

[0143] The construction module 1102 is used to determine the flip angle probability density distribution function corresponding to the radio frequency transmission field based on each group of magnetic resonance echo signals; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set;

[0144] The determination module 1103 is used to determine the distribution of the radio frequency transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0145] In one embodiment, the construction module 1102 is specifically used to obtain the joint probability density distribution function corresponding to the magnetic resonance echo signal;

[0146] Based on the joint probability density distribution function and the preset probability algorithm, a flip angle probability density distribution function is constructed.

[0147] In one embodiment, the construction module 1102 is specifically used to obtain the distribution function corresponding to the magnetic resonance echo signal, and to perform a ratio calculation on the distribution function corresponding to the magnetic resonance echo signal in each group to determine the probability density distribution function corresponding to each group of magnetic resonance echo signals.

[0148] Based on the probability density distribution functions corresponding to at least two sets of magnetic resonance echo signals, a joint probability density distribution function is constructed.

[0149] In one embodiment, the construction module 1102 is specifically used to perform an integral operation on the offset of the radio frequency transmission field contained in the joint probability density distribution function to obtain the total probability density distribution function corresponding to the magnetic resonance echo signal within a preset range of the offset.

[0150] The flip angle probability density distribution function is constructed by calculating the ratio between the joint probability density distribution function and the total probability density distribution function.

[0151] Each module in the aforementioned radio frequency emission field detection device can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0152] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 12 As shown, the computer device includes a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, mobile cellular networks, NFC (Near Field Communication), or other technologies. When executed by the processor, the computer program implements a radio frequency emission field detection method. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0153] Those skilled in the art will understand that Figure 12The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0154] In one embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the following steps:

[0155] At least two sets of magnetic resonance echo signals are acquired; each set of magnetic resonance echo signals is generated by the detection object excited by radio frequency transmission pulses with different preset flip angles, and the different preset flip angles conform to a predetermined relationship.

[0156] Based on each set of magnetic resonance echo signals, determine the flip angle probability density distribution function corresponding to the radio frequency transmission field; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantities of the magnetic resonance echo signal are set;

[0157] The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0158] In one embodiment, the processor, when executing a computer program, also performs the following steps:

[0159] Obtain the joint probability density distribution function corresponding to the magnetic resonance echo signal;

[0160] Based on the joint probability density distribution function and the preset probability algorithm, the flip angle probability density distribution function is constructed.

[0161] In one embodiment, the processor, when executing a computer program, also performs the following steps:

[0162] Obtain the distribution function corresponding to the magnetic resonance echo signal, and perform a ratio calculation on the distribution function corresponding to the magnetic resonance echo signal in each group to determine the probability density distribution function corresponding to each group of magnetic resonance echo signals.

[0163] A joint probability density distribution function is constructed based on the probability density distribution functions corresponding to at least two sets of magnetic resonance echo signals.

[0164] In one embodiment, the processor, when executing a computer program, also performs the following steps:

[0165] By integrating the offset of the radio frequency transmission field contained in the joint probability density distribution function, the total probability density distribution function corresponding to the magnetic resonance echo signal within the preset range of the offset is obtained.

[0166] The flip angle probability density function is constructed by calculating the ratio between the joint probability density function and the total probability density function.

[0167] In one embodiment, the processor, when executing a computer program, also performs the following steps:

[0168] The detection object is excited by a scanning sequence, which includes at least two sets of radio frequency emission pulse combinations, and the preset flip angles corresponding to the radio frequency emission pulse combinations conform to a predetermined relationship.

[0169] At least two sets of magnetic resonance echo signals are acquired, and each set of magnetic resonance echo signals corresponds to a set of radio frequency transmission pulse combinations.

[0170] Based on each set of magnetic resonance echo signals, determine the flip angle probability density distribution function corresponding to the radio frequency transmission field; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantities of the magnetic resonance echo signal are set;

[0171] The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal; and,

[0172] The parameters of the scanning sequence are adjusted according to the distribution of the radio frequency transmission field to obtain the target transmission field.

[0173] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0174] At least two sets of magnetic resonance echo signals are acquired; each set of magnetic resonance echo signals is generated by the detection object excited by radio frequency transmission pulses with different preset flip angles, and the different preset flip angles conform to a predetermined relationship.

[0175] Based on each set of magnetic resonance echo signals, determine the flip angle probability density distribution function corresponding to the radio frequency transmission field; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantities of the magnetic resonance echo signal are set;

[0176] The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal.

[0177] In one embodiment, when the computer program is executed by a processor, it also performs the following steps:

[0178] Obtain the joint probability density distribution function corresponding to the magnetic resonance echo signal;

[0179] Based on the joint probability density distribution function and the preset probability algorithm, the flip angle probability density distribution function is constructed.

[0180] In one embodiment, when the computer program is executed by a processor, it also performs the following steps:

[0181] Obtain the distribution function corresponding to the magnetic resonance echo signal, and perform a ratio calculation on the distribution function corresponding to the magnetic resonance echo signal in each group to determine the probability density distribution function corresponding to each group of magnetic resonance echo signals.

[0182] A joint probability density distribution function is constructed based on the probability density distribution functions corresponding to at least two sets of magnetic resonance echo signals.

[0183] In one embodiment, when the computer program is executed by a processor, it also performs the following steps:

[0184] By integrating the offset of the radio frequency transmission field contained in the joint probability density distribution function, the total probability density distribution function corresponding to the magnetic resonance echo signal within the preset range of the offset is obtained.

[0185] The flip angle probability density function is constructed by calculating the ratio between the joint probability density function and the total probability density function.

[0186] In one embodiment, when the computer program is executed by a processor, it also performs the following steps:

[0187] The detection object is excited by a scanning sequence, which includes at least two sets of radio frequency emission pulse combinations, and the preset flip angles corresponding to the radio frequency emission pulse combinations conform to a predetermined relationship.

[0188] At least two sets of magnetic resonance echo signals are acquired, and each set of magnetic resonance echo signals corresponds to a set of radio frequency transmission pulse combinations.

[0189] Based on each set of magnetic resonance echo signals, determine the flip angle probability density distribution function corresponding to the radio frequency transmission field; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantities of the magnetic resonance echo signal are set;

[0190] The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal; and,

[0191] The parameters of the scanning sequence are adjusted according to the distribution of the radio frequency transmission field to obtain the target transmission field.

[0192] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0193] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties.

[0194] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0195] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0196] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for detecting radio frequency emission fields, characterized in that, The method includes: At least two sets of magnetic resonance echo signals are acquired; each set of magnetic resonance echo signals is generated by exciting the detection object with radio frequency transmission pulses of different preset flip angles, and the different preset flip angles conform to a predetermined relationship. Obtain the joint probability density distribution function corresponding to the magnetic resonance echo signal; Based on the joint probability density distribution function and the preset probability algorithm, a flip angle probability density distribution function is constructed; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set; The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal.

2. The method according to claim 1, characterized in that, The step of obtaining the joint probability density distribution function corresponding to the magnetic resonance echo signal includes: Obtain the distribution function corresponding to the magnetic resonance echo signal, and perform a ratio calculation on the distribution function corresponding to the magnetic resonance echo signal in each group to determine the probability density distribution function corresponding to each group of magnetic resonance echo signals; A joint probability density distribution function is constructed based on the probability density distribution functions corresponding to at least two sets of magnetic resonance echo signals.

3. The method according to claim 1, characterized in that, The step of constructing the flip angle probability density distribution function based on the joint probability density distribution function and the preset probability algorithm includes: By integrating the offset of the radio frequency transmission field contained in the joint probability density distribution function, the total probability density distribution function corresponding to the magnetic resonance echo signal within a preset range of the offset is obtained. The flip angle probability density distribution function is constructed by calculating the ratio between the joint probability density distribution function and the total probability density distribution function.

4. A radio frequency transmission field correction method, characterized in that, The method includes: The detection object is excited by a scanning sequence, wherein the scanning sequence includes at least two sets of radio frequency emission pulse combinations, and the preset flip angles corresponding to the radio frequency emission pulse combinations conform to a predetermined relationship; At least two sets of magnetic resonance echo signals are acquired, and each set of magnetic resonance echo signals corresponds to a set of radio frequency transmission pulse combinations. Obtain the joint probability density distribution function corresponding to the magnetic resonance echo signal; Based on the joint probability density distribution function and the preset probability algorithm, a flip angle probability density distribution function is constructed; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set; The distribution of the radio frequency transmission field is determined based on the flip angle probability density distribution function and the magnetic resonance echo signal; and, The parameters of the scanning sequence are adjusted according to the distribution of the radio frequency transmission field to obtain the target transmission field.

5. The method according to claim 4, characterized in that, Determining the distribution of the radio frequency transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signal includes: Obtain the signal-to-signal ratio of the magnetic resonance echo signals within each group; The signal ratio is used as a known condition for solving the current RF transmission field flip angle. It is substituted into the flip angle probability density distribution function to determine the actual flip angle of the RF transmission field. The distribution of the radio frequency transmission field is determined based on the actual flip angle of the radio frequency transmission field.

6. The method according to claim 4, characterized in that, The preset flip angle of the radio frequency transmission pulse combination in the same group conforms to a linear relationship.

7. The method according to claim 4, characterized in that, The magnetic resonance echo signal includes a stimulated echo signal and a free-induction fading signal, and the characteristic quantity of the magnetic resonance echo signal is the ratio of the stimulated echo signal to the free-induction fading signal.

8. A radio frequency emission field detection device, characterized in that, The device includes: The acquisition module is used to acquire at least two sets of magnetic resonance echo signals; each set of magnetic resonance echo signals is generated by exciting the detection object with radio frequency transmission pulses of different preset flip angles, and the different preset flip angles conform to a predetermined relationship. A construction module is used to obtain the joint probability density distribution function corresponding to the magnetic resonance echo signal; and to construct the flip angle probability density distribution function based on the joint probability density distribution function and a preset probability algorithm; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the radio frequency transmission field under the condition that the characteristic quantity of the magnetic resonance echo signal is set. The determination module is used to determine the distribution of the radio frequency transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signal.

9. A magnetic resonance system, characterized in that, include: A main magnet, used to generate a main magnetic field, forms a scanning cavity; A transmitting coil is disposed within the scanning cavity and has multiple transmitting channels, each of which is capable of generating a radio frequency transmitting pulse; A receiving coil is used to acquire magnetic resonance echo signals after the radio frequency transmission pulse excites the detection object; The processor, connected to the transmitting coil and the receiving coil respectively, is used to control the transmitting coil to transmit at least two sets of radio frequency (RF) transmission pulse combinations to the detection object, wherein the preset flip angles contained in the same set of RF transmission pulse combinations conform to a predetermined relationship; to control the receiving coil to acquire at least two sets of magnetic resonance echo signals, each set of magnetic resonance echo signals corresponding to a set of RF transmission pulse combinations; to obtain the joint probability density distribution function corresponding to the magnetic resonance echo signals; to construct a flip angle probability density distribution function based on the joint probability density distribution function and a preset probability algorithm; the flip angle probability density distribution function characterizes the probability density distribution of the flip angle of the RF transmission field under a set value for the characteristic quantity of the magnetic resonance echo signal; and to determine the distribution of the RF transmission field based on the flip angle probability density distribution function and the magnetic resonance echo signals.

10. The system according to claim 9, characterized in that, The processor is also configured to generate adjustment parameters for a scanning sequence based on the distribution of the radio frequency transmission field, the adjustment parameters of which can be executed by the transmitting coil to obtain the target transmission field.

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