A method and device for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning

Abstract

The present invention discloses a method and device for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning. The spatial position monitoring module monitors the displacement and azimuth change of the object to be scanned in the scanning space, and converts the displacement and azimuth change information into parameters and then feeds them back to the sequence scanning control system in the FPGA. The sequence scanning control system calculates the scanning correction parameters according to the displacement and azimuth change parameters, and then superimposes them on the original scanning parameters for parameter modification or logical correction, so as to realize the automatic adjustment of the FOV (Field Of View) of the object to be scanned, avoid the imaging interval deviating from the part of interest due to the position change of the object to be scanned, and can well solve some actual scanning problems, such as the problem of position offset of the living body during long-time scanning of the living body, or the problem of deviation between the placement position of the object to be scanned and the predetermined reference position when the object to be scanned is transported by a conveyor belt. In these cases, there is no need to readjust the position of the object to be scanned, and the scanning FOV can be directly adjusted automatically.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic resonance, and particularly relates to a method and a device for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning. Background Art

[0002] Magnetic resonance imaging (MRI) technology, as a non-invasive diagnostic means capable of reflecting multi-dimensional information, has been widely applied in medical pathological diagnosis and basic scientific research.

[0003] In an MRI spectrometer system, during the scanning of an object to be scanned, it is required that the object to be scanned remains stationary at a preset reference position. However, in the actual scanning process, there may be situations where the object to be scanned deviates from the reference position. For example, during the long-term scanning of a living body, the living body to be scanned may shift in position, or the actual placement position of the object to be scanned transported by a conveyor belt may deviate from the fixed standard position. In these cases, if the position of the object to be scanned is not adjusted accordingly, there will be a deviation between the scanned part and the part expected to be observed. According to the existing nuclear magnetic resonance scanning technology, if these deviations are to be eliminated, it is necessary to readjust the position of the object to be scanned, or to perform a positioning film scan on the living body to be scanned again, or to re-place the object to be scanned to coincide with the reference position. After re-determining the position of the object to be scanned in this way, the formal scanning is restarted. Sometimes, the scanning process even needs to be interrupted and redone, which is very time-consuming and cannot guarantee that the object to be scanned will not shift in position again during the subsequent scanning process. Summary of the Invention

[0004] Aiming at the deficiencies of the existing scanning technology, the present invention provides a method and a device for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning. When the placement position of the object to be scanned deviates from the preset reference position, or when the object to be scanned shifts in position during the scanning process, etc., by adjusting the original parameters in real time and appropriately correcting the logical gradient, it is not necessary to re-place the object to be scanned and the scanning process is not interrupted. The system automatically adjusts the FOV to complete the scanning of the correct part of the object to be scanned. After the implementation of this method, the scanning process does not increase the time, and at the same time, the requirement for the scanned object to remain stationary is reduced. It is particularly suitable for scanning living bodies such as infants or animals that are inconvenient to keep stationary. For some objects to be scanned that need to be placed at a fixed reference position for scanning, the placement position requirements are not so strict, which can improve the scanning efficiency. Moreover, the adjustment of the FOV is made more precise by using a digital processing method.

[0005] In order to achieve the above objectives, the present invention is realized through the following technical solutions:

[0006] The spatial position monitoring module monitors the displacement and azimuth change of the object being scanned relative to the reference position in real time through a camera, and gives specific angle parameters and translation parameters. The acquisition of the reference position can be to record the current position and direction of the object being scanned as the reference position during sequential positioning scanning, or a fixed standard reference position preset in the system. Each time the sequential scanning is switched, the position and direction of the object being scanned are re-photographed, and the change in the position of the object being scanned relative to the reference position is calculated at this time. At the same time, the position change information is converted into digital position change parameters, including parameters for translation along the coordinate axes and angle parameters for rotation around the three coordinate axes.

[0007] The sequential scanning control system includes a trigonometric function calculation module, a rotation matrix calculation module, and a translation parameter calculation module. The trigonometric function calculation module calculates the trigonometric function values (sin values and cos values) according to the angle change parameters fed back by the spatial position monitoring module. The rotation matrix calculation module can calculate the rotation matrix for angle rotation of the coordinate axes based on the trigonometric function values. The translation parameter calculation module can calculate the frequency value and phase value sizes that the transmitting and receiving modules need to adjust according to the translation parameters.

[0008] The parameter adjustment and correction module includes a logical gradient rotation module and a transmitting and receiving adjustment module. The logical gradient rotation module completes the rotation matrix adjustment of the logical gradient waveform. The transmitting and receiving module can adjust the transmitting frequency value or the receiving frequency value and phase value to change the slice selection and position of the object being scanned, so as to complete the adjustment of the FOV of the object being scanned.

[0009] The trigonometric function calculation module has the following method:

[0010] The cordic algorithm is adopted. The Cordic algorithm solves trigonometric functions by means of iterative rotation approximation, and solves the sine (sin) and cosine (cos) trigonometric function values of the angle change parameters through iterative rotation approximation. In implementation, only a set of shift registers and adders need to be multiplexed to complete the calculation of trigonometric functions, and the hardware overhead is very small, which is suitable for applications in occasions where the real-time requirement for calculation is not high. The coordinate point calculation formula obtained after n times of rotation iteration of the algorithm is:

[0011] X n = X0cos(θ) - Y0sin(θ) = K·cos(θ)·(X0 - Y0tan(θ))

[0012] Y n = Y0cos(θ) + X0sin(θ) = K·cos(θ)·(Y0 + X0tan(θ))

[0013] where (X0, Y0) is the starting coordinate of the iterative rotation, (Xn , Y n ) represents the coordinate point after multiple rotation iterations. θ is the preset rotation angle, and K is the scaling factor, representing the change in the modulus of the vector during the rotation process. Its magnitude is related to the number of iterations. If the number of iterations is fixed, then K is a constant and can be obtained by looking up a table.

[0014] If the starting point (X0, Y0) is the unit vector on the X-axis, then after multiple iterations, the angle rotates to the predetermined angle θ. After the modulus of the rotated vector is corrected by the scaling factor, a new unit vector (X n , Y n )'s projections on the abscissa and ordinate respectively correspond to the cos(θ) value and sin(θ) value of the rotation angle θ.

[0015] The method of the rotation matrix calculation module is as follows:

[0016] Based on the trigonometric function values calculated by the trigonometric function calculation module, the matrix expression for the coordinate axis rotation operation can be obtained. The rotation operation can be completed by matrix multiplication. The three rotation matrices R x , R y and R z for the rotation operations along the X, Y, and Z coordinate axes in sequence can be used to obtain the rotation matrix R xyz for the rotation operation of the object to be scanned in the entire coordinate system. The method is as follows:

[0017] First, rotate by an angle α around the X-axis. The method is as follows:

[0018] y′ = ycosα - zsinα

[0019] z′ = ysinα + zcosα

[0020] x′ = x

[0021] where (x, y, z) are the coordinate axes before rotation, (x′, y′, z′) are the coordinate axes after rotation, and α is the angle by which the object to be scanned rotates around the X-axis in the original coordinate system. Its rotation direction follows the right-hand rule and can be described by the matrix expression:

[0022]

[0023] Then, rotate by an angle β around the y-axis. The method is as follows:

[0024] z′ = zcosβ - xsinβ

[0025] x′ = zsinβ + xcosβ

[0026] y′ = y

[0027] Where (x, y, z) are the coordinate axes before rotation, (x′, y′, z′) are the coordinate axes after rotation, β is the angle by which the scanned object rotates around the y-axis in the original coordinate system, and its rotation direction follows the right-hand rule. It is described by the matrix expression as follows:

[0028]

[0029] Then rotate by an angle γ about the Z axis. The method is as follows:

[0030] x′ = x cosγ - y sinγ

[0031] y′ = x sinγ + y cosγ

[0032] ′

[0033] z = z

[0034] Where (x, y, z) are the coordinate axes before rotation, (x′, y′, z′) are the coordinate axes after rotation, γ is the angle by which the scanned object rotates around the z-axis in the original coordinate system, and its rotation direction follows the right-hand rule. It is described by the matrix expression as follows:

[0035]

[0036] The rotations of the X, Y, and Z axes can be completed by three rotations using three rotation matrices. The final rotation result can be obtained by multiplying the three rotation matrices to get a total rotation matrix R xyz Implement through one rotation:

[0037] R xyz = R x (α)R y (β)R z (γ)

[0038]

[0039] For the convenience of subsequent calculation and expression, use h mn to represent the elements of the rotation matrix R xyz During the subsequent automatic adjustment of the rotation angle, multiplying by the logical gradient and the rotation matrix R xyz can achieve the adjustment of the angular offset of the three coordinate axes.

[0040] The translation parameter calculation module includes a multiplier, an adder, and a divider, and calculates the projection change parameters of the scanned object on the new coordinate axes. The method is as follows:

[0041] Assume D x , D y , D zThey are the projections of the object to be scanned on the coordinate axes of the reference position, i.e., the original translation parameters. Assume that after the rotation matrix R xyz In the new logical gradient coordinate system after transformation, the offset value of the gradient slice selection direction in the new logical gradient coordinate system is D gsoff , and the offset value in the frequency encoding direction is D groff , and the offset value in the phase encoding direction is D gpoff . According to the above-mentioned angular rotation matrix R xyz , the translation value D on the original coordinate axes x , D y , D z and the projection translation values on the new coordinate axes after matrix rotation satisfy the following relationship:

[0042]

[0043] Solving the equation gives:

[0044]

[0045]

[0046]

[0047] According to the displacement projection parameters D on the three coordinate axes gsoff , D groff , D gpoff , it is necessary to adjust the transmitted or received frequency or phase respectively to achieve the adjustment purpose.

[0048] The logical gradient rotation module includes a multiplier and an adder, which perform matrix multiplication on the three input logical gradients din_read, din_phase, din_slice and the rotation matrix R xyz to achieve the purpose of adjusting the orientation of the logical gradient. The method is:

[0049] [dout_x, dout_y, dout_z] = [din_read, din_phase, din_slice] × R xyz

[0050] where dout_x, dout_y, dout_z represent the logical gradient waveforms after the rotation matrix adjustment. Rearranging the above formula gives:

[0051] dout_x = h 11 ·din_read + h 21 ·din_phase + h 31 ·din_slice

[0052] dout_y = h 12 ·din_read + h 22 ·din_phase + h 32 ·din_slice

[0053] dout_z = h 13 ·din_read + h 23 ·din_phase + h 33 ·din_slice

[0054] After the logical gradient waveforms din_read, din_phase, and din_slice are processed by the above matrix rotation adjustment, they can be correctly projected onto the physical gradient direction of the scanned volume after shifting.

[0055] The transmit-receive adjustment module adjusts the transmit frequency or receive frequency value or receive phase value through the displacement projection parameters D gsoff , D groff , D gpoff on the three coordinate axes of the scanned volume displacement in the new coordinate system. The method is as follows:

[0056] When D gsoff ≠ 0, it is necessary to adjust the frequency value of the transmit pulse in the transmit module:

[0057] f tx = f tx0 + γ·Gs·D gsoff

[0058] where f tx0 is the original transmit frequency, γ is the gyromagnetic ratio, and Gs is the slice selection gradient.

[0059] When D groff ≠ 0, it is necessary to adjust the receive frequency value in the receive module:

[0060] f rx = f rx0 + γ·Gr·D groff

[0061] where f rx0 is the original receive frequency, γ is the gyromagnetic ratio, and Gr is the readout gradient.

[0062] When D gpoff ≠ 0, it is necessary to adjust the receive phase value in the receive module:

[0063] θ rx = θ rx0 + γ·Gp·D gpoff ·T

[0064] where θrx0 The original received phase, γ is the gyromagnetic ratio, Gp is the phase gradient, and T is the duration of phase encoding.

[0065] By calculating the adjusted transmit frequency, receive frequency, or receive phase using the above formula, the scanned slice and position desired by the user can be correctly selected.

[0066] In summary, the present invention has the following advantages and effects:

[0067] 1. It can monitor the change of the scanned object's position in real time and automatically adjust the FOV, without the need to interrupt the scan for repositioning, saving scan time.

[0068] 2. It can monitor the change of the scanned object's position in real time and perform automatic adjustment, making the scanned part consistent with the part to be observed.

[0069] 3. It uses a digital processing method for adjustment, with high precision. The adjustment part of the module is implemented using multipliers and adders in the FPGA, consuming relatively few logic resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a system structure diagram of the present invention DETAILED DESCRIPTION OF THE EMBODIMENTS

[0071] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention.

[0072] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0073] As Figure 1 shown, a method for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning according to an embodiment of the present invention includes a processing of a three-eye camera monitoring module and a field programmable gate array (FPGA, Field-Programmable Gate Array) of the Xilinx 7 series model. The FPGA includes: a sequence scan control system and a parameter adjustment and correction module.

[0074] In this embodiment, all modules operate in a pipelined manner. Except for the preset parameter values, the initial values of all registers are 0. All operations in this embodiment are completed under a 100 MHz clock, and the clock period is 10 ns. The working process of the entire device starts from scanning the positioning sheet. The spatial position monitoring module takes a photo as the reference position photo for judging subsequent position changes. During the formal scanning process, a real-time position photo of the object to be scanned is taken before each switching of the scanning sequence. By comparing the latest position photo with the reference position photo, the position offset of the object to be scanned relative to the scanning positioning sheet is calculated and converted into digital angular parameters and translation parameters for adjustment.

[0075] Before each switching of the scanning sequence for scanning, the rotation matrix calculation module receives the angular parameters and translation parameters sent by the spatial position monitoring module and performs an adjustment parameter calculation process. First, the trigonometric function calculation module converts the offset angular parameters into corresponding sine (sin) and cosine (cos) trigonometric function values. Specifically, the Cordic algorithm is used. Only a group of shift registers and adders need to be reused, and the trigonometric functions can be solved by the iterative rotation approximation method. The formula after n iterations is:

[0076] X n = X0cos(θ) - Y0sin(θ) = K·cos(θ)·(X0 - Y0tan(θ))

[0077] Y n = Y0cos(θ) + X0sin(θ) = K·cos(θ)·(Y0 + X0tan(θ))

[0078] where (X0, Y0) is the unit vector on the X-axis and is the starting point of the iterative rotation, θ is the preset rotation angle, (X n , Y n ) represents the coordinate vector after the modulus value is corrected by the scaling factor after multiple rotation iterations. K is the scaling factor, which represents the change amount of the vector modulus value during the rotation process. Its magnitude is related to the number of iterations. If the number of iterations is fixed, then K is a constant and can be obtained by looking up a table.

[0079] According to the system accuracy requirements, the number of Cordic iterations can be modified to meet the accuracy requirements. In digital signal processing, for a 20-bit width and 16 iterations of calculation of sin and cos values, the error is less than 0.0004%. When the number of iterations is determined, the K value is also determined. When n = 16, the constant K = 0.6073 is obtained by looking up a table.

[0080] If the starting point is the unit vector (1, 0) on the X-axis, after multiple iterations, the angle rotates to the predetermined angle θ, and the projections of the unit vector obtained after correcting the modulus value by the scaling factor on the abscissa and ordinate are the cos(θ) value and sin(θ) value of the angle θ, respectively.

[0081] After obtaining the cos(θ) value and sin(θ) value of the angle θ, the rotation matrix R is calculated according to the translation parameters. xyz 。

[0082] R xyz =R x (α)R y (β)R z (γ)

[0083]

[0084] The rotation matrix R needs to be updated before each scan sequence switch. xyz , and the update period of the matrix is the time interval of one scan sequence switch. The rotation matrix R xyz needs to be updated before the start of each sequence scan and remains unchanged during the entire sequence scan.

[0085] The logical gradient processing module works during each sequence scan, and its working clock is 100 MHz. It performs matrix multiplication on the three input logical gradient waveforms din_read, din_phase, din_slice and the rotation matrix R xyz to achieve the purpose of adjusting the logical gradient waveform to an angle:

[0086] [dout_x, dout_y, dout_z] = [din_read, din_phase, din_slice] × R xyz

[0087] where dout_x, dout_y, dout_z represent the logical gradient waveforms after the rotation matrix adjustment. Rearranging the above formula gives:

[0088] dout_x = h 11 ·din_read + h 21 ·din_phase + h 31 ·din_slice

[0089] dout_y = h 12 ·din_read + h 22 ·din_phase + h 32 ·din_slice

[0090] dout_z = h 13 ·din_read + h 23 ·din_phase + h 33 ·din_slice

[0091] After the logical gradient waveform is processed by the above matrix multiplication, it can be correctly projected onto the physical gradient direction in the new rotating coordinate system. Since the update period of the logical gradients din_read, din_phase, and din_slice is 1 us and the working clock of the logical gradient processing module is 100 MHz, only one set of multipliers and adders is needed when calculating the matrix multiplication, and the matrix multiplication operation can be completed by using the time-division multiplexing method, saving logical resources.

[0092] For the adjustment of position translation, the transmitted or received frequency value or phase value needs to be modified. The specific operation is based on the displacement projection parameters D of the scanned object displacement on the three coordinate axes in the new coordinate system gsoff , D groff , D gpoff to adjust the transmitted frequency value, received frequency value, and received phase value respectively:

[0093] When D gsoff ≠ 0, the frequency value of the transmitted pulse in the transmitting module needs to be adjusted:

[0094] f tx = f tx0 + γ·Gs·D gsoff

[0095] where f tx0 is the original transmitted frequency, the parameter is set according to the sequence, γ is the gyromagnetic ratio, and Gs is the slice selection gradient.

[0096] When D groff ≠ 0, the received frequency value in the receiving module needs to be adjusted;

[0097] f rx = f rx0 + γ·Gr·D groff

[0098] where f rx0 is the original received frequency, the parameter is set according to the sequence, γ is the gyromagnetic ratio, and Gr is the readout gradient.

[0099] When D gpoff ≠ 0, the received phase value in the receiving module needs to be adjusted:

[0100] θ rx = θ rx0 + γ·Gp·D gpoff ·T

[0101] where θ rx0 is the original received phase, the parameter is set according to the sequence, γ is the gyromagnetic ratio, Gp is the phase gradient, and T is the duration of phase encoding.

[0102] The adjustment method is to update the scanning parameters and superimpose the calculated changed parameters on the original scanning parameters. The adjustment process can be achieved without additional hardware logic here.

Claims

1. A device suitable for automatically adjusting the FOV for nuclear magnetic resonance scanning, characterized in that, Including: A spatial position monitoring module, which is used to monitor the displacement and azimuth change of the object to be scanned relative to the reference position in real time through a camera during the scanning process, and give specific angle parameters and translation parameters; A sequential scanning control system, which is used to calculate the correction parameters required for adjustment and correction according to the position change parameters fed back by the spatial position monitoring module, and output them to the parameter adjustment and correction module for adjustment; A parameter adjustment and correction module, which is used to receive the correction parameters provided by the sequential scanning control system, superimpose them on the initial scanning parameters set in sequence, and complete the adjustment of the FOV of the scanned object by logical operation or by adjusting frequency or phase parameters. The sequence scanning control system includes a rotation matrix calculation module and a translation parameter calculation module. The rotation matrix calculation module is used to calculate the rotation matrix for adjusting the angular change, and the translation parameter calculation module is used to calculate the translation parameter for adjusting the displacement change. The rotation matrix calculation module consists of a trigonometric function calculation module and a matrix multiplication calculation module, and is used to calculate the rotation matrix R required for adjusting the logical gradient xyz , and the translation parameter calculation module is used to calculate the frequency or phase parameter that needs to be adjusted for the transmitting and receiving modules according to the translation parameter; The trigonometric function values corresponding to the three offset angles of the scanned object calculated according to the CORDIC algorithm are used to calculate the matrix expression of the coordinate axis rotation operation. The rotation operation is completed by matrix multiplication. The three rotation matrices R x , R y and R z are used to find the rotation matrix R xyz of the rotation operation of the scanned object in the entire coordinate system. Multiply the logical gradient by the rotation matrix R xyz to realize the adjustment of the angular offsets of the three angular coordinate axes.

2. The device for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning according to claim 1, wherein: The spatial position monitoring module includes a three-eye camera and an image processing module. The three-eye camera is used to monitor the position of the object to be scanned in multiple directions, and the image processing module is used to compare and process the position image taken later with the reference position image to obtain the position offset of the object to be scanned in the X, Y, and Z coordinate axes directions, including angle rotation and position translation, and convert this information into digital angle parameters and translation parameters.

3. The device for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning according to claim 1, characterized in that: The parameter adjustment and correction module includes a logical gradient adjustment module and a transmission and reception adjustment module. The logical gradient adjustment module is used to correctly project the logical gradient onto the physical gradient, and the transmission and reception adjustment module is used to correctly select the layer and position desired by the user for scanning.

4. A method for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning, implemented based on the device for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning according to any one of claims 1-3, characterized in that: The trigonometric function value calculation module uses the cordic algorithm to solve the sine and cosine values of the trigonometric functions of the angle. The coordinate point calculation formula obtained after n times of rotation iteration of the algorithm is: X n = X0cos(θ) - Y0sin(θ) = K·cos(θ)·(X0 - Y0tan(θ)) Y n = Y0cos(θ) + X0sin(θ) = K·cos(θ)·(Y0 + X0tan(θ)) Among them, (X0, Y0) is the starting coordinate of the iterative rotation, and (X n , Y n ) represents the coordinate point after multiple rotation iterations. θ is the preset rotation angle, and K is the scaling factor, which represents the change amount of the vector modulus during the rotation. Its magnitude is related to the number of iterations. If the number of iterations is fixed, then K is a constant and can be obtained by looking up a table; The trigonometric function values corresponding to the three offset angles of the scanned object calculated according to the CORDIC algorithm are used to calculate the matrix expression of the coordinate axis rotation operation. The rotation operation is completed by matrix multiplication. The three rotation matrices R for the rotation operations are performed successively along the three coordinate axes X, Y, and Z x , R y and R z . The rotation matrix R of the rotation operation of the scanned object in the entire coordinate system is obtained xyz The method is as follows: First, rotate by an angle α around the X axis. The method is: y′ = ycosα - zsinα z′ = ysinα + zcosα x′ = x where (x, y, z) are the coordinate axes before rotation, (x′, y′, z′) are the coordinate axes after rotation, and α is the angle of rotation of the object to be scanned around the X axis in the original coordinate. It is described by the rotation matrix expression as: Then, rotate by an angle β around the y axis. The method is: z′ = zcosβ - xsinβ x′ = zsinβ + xcosβ y′ = y where (x, y, z) are the coordinate axes before rotation, (x′, y′, z′) are the coordinate axes after rotation, and β is the angle of rotation of the object to be scanned around the y axis in the original coordinate. It is described by the rotation matrix expression as: Then, rotate by an angle γ around the Z axis. The method is: x′ = xcosγ - ysinγ y′ = xsinγ + ycosγ z′ = z where (x, y, z) are the coordinate axes before rotation, (x′, y′, z′) are the coordinate axes after rotation, and γ is the angle of rotation of the object to be scanned around the z axis in the original coordinate. It is described by the rotation matrix expression as: The rotation of the X, Y, and Z axes can be completed by rotating three times using three rotation matrices. According to the rules of matrix multiplication, the final rotation result can be obtained by multiplying three single-rotation matrices to get a total rotation matrix R xyz , and the method is as follows: Use h mn to represent each element of the rotation matrix R xyz During the automatic adjustment of the rotation process, multiplying by the logical gradient and the rotation matrix R xyz can correct the angular offsets of the three coordinate axes.

5. The method for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning according to claim 4, characterized in that: Calculate the parameters of the translation parameters of the object to be scanned in the original coordinate system projected onto the new coordinate axes. The calculation method is: Assume D x , D y , D z are respectively the projections of the object to be scanned on the coordinate axes of the reference position, that is, the original translation parameters. Assume that in the new logical gradient coordinate system after transformation by the rotation matrix R xyz , the gradient slice selection direction offset value in the new logical gradient coordinate system is D gsoff , the offset value in the frequency encoding direction is D groff , and the offset value in the phase encoding direction is D gpoff ; According to the above rotation matrix R xyz , the translation value D x , D y , D z on the original coordinate axes and the projection translation values on the new coordinate axes after matrix rotation satisfy the following relationship: Solving the equation gives: According to the displacement projection parameters D on the three coordinate axes in the new coordinate system gsoff , D groff , D gpoff , the adjustment purpose is achieved by adjusting the transmitted or received frequency value or phase value.

6. The method for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning according to claim 5, characterized in that: Multiply the input three-way logical gradients din_read, din_phase, din_slice and the rotation matrix R xyz Perform matrix multiplication to achieve rotation adjustment of the orientation of the logical gradient. The method is as follows: [dout_x, dout_y, dout_z] = [din_read, din_phase, din_slice] × R xyz where dout_x, dout_y, dout_z represent the logical gradient waveforms after the rotation matrix adjustment. Rearranging the above formula gives: dout_x = h 11 ·din_read + h 21 ·din_phase + h 31 ·din_slice dout_y = h 12 ·din_read + h 22 ·din_phase + h 32 ·din_slice dout_z = h 13 ·din_read + h 23 ·din_phase + h 33 ·din_slice After the logical gradient waveforms din_read, din_phase, and din_slice are processed by the above matrix rotation, they can be correctly projected onto the physical gradient directions in the new rotated coordinate system.

7. The method for automatically adjusting the FOV applicable to nuclear magnetic resonance scanning according to claim 6, characterized in that: According to the displacement projection parameters D of the calculated displacement parameters of the object to be scanned on the three coordinate axes in the new coordinate system gsoff , D groff , D gpoff , the value is used to adjust the transmission frequency or the reception frequency or the reception phase by superimposing it on the initial parameters. The method is as follows: When D gsoff ≠ 0, it is necessary to adjust the frequency value of the emission pulse in the emission module: f tx = f tx0 + γ·Gs·D gsoff where f tx0 is the original emission frequency, γ is the gyromagnetic ratio, and Gs is the slice selection gradient; When D groff ≠ 0, it is necessary to adjust the received frequency value in the receiving module: f rx = f rx0 + γ·Gr·D groff where f rx0 is the original received frequency, γ is the gyromagnetic ratio, and Gr is the readout gradient; When D gpoff ≠ 0, it is necessary to adjust the reception phase value in the reception module: θ rx = θ rx0 + γ·Gp·D gpoff ·T where θ rx0 is the original received phase, γ is the gyromagnetic ratio, Gp is the phase gradient, and T is the duration of phase encoding; By calculating the adjusted transmit frequency, receive frequency, or receive phase using the above formula, the scan planes and positions that the user expects to see can be correctly selected.

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