Magnetic resonance arterial blood flow mute marking method and system, medium and electronic equipment

Abstract

The invention discloses a magnetic resonance arterial blood flow mute marking method and system, a medium and electronic equipment, and belongs to the technical field of magnetic resonance. In a marking period, a triangular gradient is used for replacing a traditional layer selection trapezoidal gradient and also replacing a triangular reunion gradient, and an average gradient required by a blood flow reversal condition is realized through a difference between paired triangular gradients with positive and negative amplitudes. Similarly, in a contrast period, a triangular gradient is used for replacing a trapezoidal gradient and a triangular gradient in a traditional method, but the average gradient of a triangular gradient sequence is controlled to be zero. According to the method, magnetic resonance artery blood flow marking is achieved through non-reunion gradient, and acoustic noise of blood flow marking can be greatly reduced.

Description

Technical Field

[0001] The invention belongs to the field of magnetic resonance technology, and in particular relates to a magnetic resonance arterial blood flow silent marking method, system, medium and electronic equipment. Background Art

[0002] Arterial spin labeling (ASL) as a non-invasive magnetic resonance blood perfusion imaging method has been widely used in clinical and scientific research. Its basic principle is to use water molecules in the arteries as endogenous tracers, invert the magnetic resonance signals of water molecules through radio frequency pulses, and then track the flow of water molecules. When water molecules with inverted signals flow into human tissues (such as gray matter in the brain), they will partially offset the signals of water molecules in the tissues, thereby reducing the overall signal of the tissues. By calculating the changes in the signals, the exchange amount of water molecules can be obtained, and the blood perfusion situation can be obtained, which is called cerebral blood perfusion in the brain.

[0003] The key technology in arterial spin labeling imaging is how to achieve the inversion of arterial blood flow signals. This technology adopts the adiabatic pulsed radio frequency design method (Adiabatic RF) and is implemented using the flow-driven inversion principle. Specifically, when the blood flows through the center of the gradient magnetic field Gz, it will experience the positive (along the main magnetic field direction) and reverse (opposite to the main magnetic field) in space. Due to the gradient design of the magnetic field, the magnetic field strength felt by the blood flow at a position far away from the center of the magnetic field is relatively large. This magnetic field is recorded as Bz. At the same time, a horizontal radio frequency (RF) magnetic field B1 is applied during the time when the blood flows. The two magnetic fields B1 and Bz are added in a vector manner to form the final magnetic field Beff, and the direction of the magnetic field gradually changes from positive to reverse as the blood flow moves, such as Figure 1 As shown in Figure 2, water molecules in the blood flow rotate around Beff under the influence of the magnetic field and gradually reverse with it.

[0004] The third generation of blood flow labeling method is currently widely used: pseudo continuous blood flow labeling (pCASL). Figure 1 The continuous radio frequency RF and gradient Gz are divided into rapidly switching waveforms, such as Figure 2 As shown, this can meet the limitations of the magnetic resonance instrument hardware (mainly the RF power amplifier), and each switching cycle However, the gradient magnetic field needs to increase the current to generate the magnetic field when changing, and it will also generate noise, especially when the gradient field changes rapidly (corresponding to Figure 2The rising and falling edges of the green trapezoid and triangle in the middle) produce strong noise, and the faster the gradient switching rate, the greater the noise generated. This can be uncomfortable for patients and may introduce interference signals in resting-state brain functional imaging. According to the international guidelines for arterial spin labeling imaging, the blood flow inversion design implements ultra-short gradients (about 500us each) with trapezoids (for selection of the labeling plane) and triangles (for refocusing of the signal) at the maximum switching rate, thus generating strong noise.

[0005] In view of the above problems, it is urgent to design a blood flow labeling technology that reduces noise. Summary of the invention

[0006] The purpose of the present invention is to solve the problem that the blood flow labeling process of arterial spin labeling imaging in the prior art introduces noise, and to provide a magnetic resonance arterial blood flow silent labeling method, system, medium and electronic equipment.

[0007] The specific technical solutions adopted by the present invention are as follows:

[0008] In a first aspect, the present invention provides a method for magnetic resonance arterial blood flow silent marking, which is performed by alternately performing a marking cycle and a control cycle during a scanning process;

[0009] In the labeling period, a first pseudo-continuous pulse chain consisting of a series of radio frequency pulses with equal time intervals is applied to label the spin protons in the arterial blood, and the phase of the radio frequency pulses in the first pseudo-continuous pulse chain is modulated alternately at 0° and 180°, and a first triangular gradient sequence with alternating reverse amplitudes is applied at the same time; the triangular gradients in the first triangular gradient sequence correspond to the radio frequency pulses in the first pseudo-continuous pulse chain and are applied synchronously, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative and the gradient amplitudes are different, and the average gradient of the first triangular gradient sequence is not 0;

[0010] In the control period, a second pseudo-continuous pulse chain is applied, which has the same parameters as the first pseudo-continuous pulse chain except the phase, and the phase of the radio frequency pulse in the first pseudo-continuous pulse chain is constant at 0°, and a second triangular gradient sequence is applied in an alternating reverse direction; the triangular gradients in the second triangular gradient sequence are applied synchronously with the radio frequency pulses in the second pseudo-continuous pulse chain in a one-to-one correspondence, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative, and the gradient amplitudes are the same, and the average gradient of the second triangular gradient sequence is 0.

[0011] As a preferred embodiment of the first aspect, in the first triangular gradient sequence, the gradient amplitudes of two adjacent triangular gradients are 8 mT / m and -6 mT / m respectively, and the average gradient is 0.5 mT / m.

[0012] As a preferred embodiment of the first aspect, in the second triangular gradient sequence, the gradient amplitudes of two adjacent triangular gradients are 8 mT / m and -8 mT / m respectively, and the average gradient is 0 mT / m.

[0013] As a preferred embodiment of the above-mentioned first aspect, the period of the RF pulses in the first pseudo-continuous pulse chain and the second pseudo-continuous pulse chain is 1000 µs, the duration of a single RF pulse is 500 µs, and the average intensity of the RF pulse is 1.7uT; the duration of the triangular gradients in the first triangular gradient sequence and the second triangular gradient sequence is 1000 µs.

[0014] As a preferred embodiment of the first aspect, a marking cycle module and a control cycle module are alternately executed during the scanning process;

[0015] The marking period module is used to apply a first pseudo-continuous pulse chain consisting of a series of radio frequency pulses with equal time intervals to mark the spin protons in arterial blood during the marking period, and the radio frequency pulse phases in the first pseudo-continuous pulse chain are alternately modulated at 0° and 180°, and a first triangular gradient sequence with alternating reverse amplitudes is applied at the same time; the triangular gradients in the first triangular gradient sequence are synchronously applied in a one-to-one correspondence with the radio frequency pulses in the first pseudo-continuous pulse chain, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative and the gradient amplitudes are different, and the average gradient of the first triangular gradient sequence is not 0;

[0016] The control cycle module is used to apply a second pseudo-continuous pulse chain in the control cycle, which has the same parameters as the first pseudo-continuous pulse chain except the phase, and the phase of the radio frequency pulse in the first pseudo-continuous pulse chain is constant at 0°, and at the same time apply a second triangular gradient sequence that is alternating in the opposite direction; the triangular gradients in the second triangular gradient sequence are synchronously applied in a one-to-one correspondence with the radio frequency pulses in the second pseudo-continuous pulse chain, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative and the gradient amplitudes are the same, and the average gradient of the second triangular gradient sequence is 0.

[0017] In a second aspect, the present invention provides a method for optimizing parameters of a magnetic resonance arterial blood flow silent marking system as described in any one of the solutions of the first aspect, comprising:

[0018] S1. For the marking period module, the period of the radio frequency pulse in the first pseudo-continuous pulse chain, the radio frequency pulse intensity, the duration of a single radio frequency pulse, and the positive gradient amplitude, negative gradient amplitude, and duration of a single triangle gradient of two adjacent triangle gradients in the first triangle gradient sequence are used as the first optimization parameter combination. For each feasible solution of the first optimization parameter combination in the solution space, the signal value of the hydrogen atoms on the water molecules in the arterial blood flow is calculated by numerical simulation, and the negative maximization of the signal value is taken as the goal to obtain the optimal solution of the first optimization parameter combination and use it as the radio frequency pulse and triangle gradient parameters in the marking period module;

[0019] S2. For the control period module, the period of the RF pulse in the second pseudo-continuous pulse chain, the RF pulse intensity, the duration of a single RF pulse, and the positive gradient amplitude, negative gradient amplitude, and duration of a single triangular gradient of two adjacent triangular gradients in the second triangular gradient sequence are used as the second optimization parameter combination. For each set of feasible solutions of the second optimization parameter combination in the solution space, the signal values ​​of hydrogen atoms on water molecules in the arterial blood flow are calculated through numerical simulation. With the goal of maximizing the positive direction of the signal value, the optimal solution of the second optimization parameter combination is obtained and used as the RF pulse and triangular gradient parameters in the control period module.

[0020] In a third aspect, the present invention provides an arterial spin labeling imaging method, which alternately executes labeling cycles and control cycles during scanning according to the magnetic resonance arterial blood flow silent labeling method as described in any one of the schemes of the first aspect above, and waits for the labeled blood to flow into the imaging area and acquires a labeled image after each labeling cycle, and waits for the labeled blood to flow into the imaging area and acquires a reference image after each control cycle.

[0021] In a fourth aspect, the present invention provides a computer program product, including a computer program / instruction, which, when executed by a processor, can implement the magnetic resonance arterial blood flow silent marking method as described in any one of the schemes of the first aspect above.

[0022] In a fifth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the magnetic resonance arterial blood flow silent marking method as described in any one of the schemes in the first aspect above can be implemented.

[0023] In a sixth aspect, the present invention provides a computer electronic device comprising a memory and a processor;

[0024] The memory is used to store computer programs;

[0025] The processor is used to implement the magnetic resonance arterial blood flow silent marking method as described in any one of the solutions of the first aspect when executing the computer program.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] In the labeling cycle, the present invention uses a triangular gradient to replace the traditional layer-selected trapezoidal gradient, and also replaces the triangular refocusing gradient, and the average gradient required for the blood flow reversal condition is achieved by the difference between the paired triangular gradients with positive and negative amplitudes. Similarly, in the control cycle, a triangular gradient is also used to replace the trapezoidal gradient and the triangular gradient in the traditional practice, but the average gradient of the triangular gradient sequence is controlled to zero. The present invention uses a non-refocusing gradient to achieve magnetic resonance arterial blood flow labeling, which can greatly reduce the acoustic noise of blood flow labeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the principle of pseudo-continuous blood flow labeling technology pCASL;

[0029] Figure 2 Schematic diagram of the radio frequency pulses and gradients of the pCASL sequence;

[0030] Figure 3 Schematic diagram of the radio frequency pulses and gradients of the labeled and control parts in the pCASL sequence;

[0031] Figure 4 A schematic diagram of the radio frequency pulses and gradients of the labeled portion and the control portion in the silent pCASL sequence of the present invention;

[0032] Figure 5 This is a schematic diagram of the module composition of the magnetic resonance arterial blood flow silent marking system;

[0033] Figure 6 Schematic diagram of the silent pCASL sequence under the "optimal parameter group" in an embodiment of the present invention;

[0034] Figure 7 The results of different links in the embodiment of the present invention, wherein a) is the layer selection mark plane, b) is the result of non-resonance frequency simulation, c) is the average signal curve of 5 subjects, and d) is the human body test result of non-resonance frequency test;

[0035] Figure 8 is the noise test result of the silent pCASL sequence in the embodiment of the present invention;

[0036] Fig. 9The quality comparison of blood perfusion images finally obtained on multiple subjects in the embodiment of the present invention is shown in FIG. 1 , wherein a) is an image obtained by a silent pCASL sequence, and b) is an image obtained by a traditional pCASL sequence;

[0037] Fig.10 A schematic diagram of the components of computer electronic equipment. DETAILED DESCRIPTION

[0038] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0039] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0040] In the description of the present invention, it is to be understood that when an element is considered to be "connected" to another element, it may be directly connected to the other element or indirectly connected, that is, there are intermediate elements. On the contrary, when an element is said to be "directly" connected to another element, there are no intermediate elements.

[0041] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for the purpose of distinguishing descriptions, and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0042] In arterial spin labeling (ASL), conventional pseudo continuous labeling (pCASL) sequences such as Figure 3 As shown in the figure, for each RF pulse (blue part), a positive trapezoidal gradient for marking plane selection and a negative triangular gradient (red part) for signal refocusing are designed separately, that is, a trapezoidal gradient and a triangular gradient are applied in one RF pulse cycle. However, due to the maximum gradient conversion rate used in blood flow reversal, this sequence will produce relatively strong noise in practical applications, and the faster the gradient conversion rate, the greater the noise generated.

[0043] In a preferred embodiment of the present invention, in order to solve the noise problem in the traditional pCASL sequence, a magnetic resonance arterial blood flow silent marking method is provided. The marking method is achieved by redesigning the Figure 4 Similar to the conventional pCASL sequence, the silent pCASL sequence designed in the present invention also needs to alternately execute the label cycle and the control cycle during the scanning process, but the specific pulse and gradient forms in the label cycle and the control cycle are different.

[0044] Continue to see Figure 4 As shown in the marked part in , in the marking period of the silent pCASL sequence, a first pseudo-continuous pulse chain consisting of a series of RF pulses with equal time intervals needs to be applied to mark the spinning protons in the arterial blood, and the RF pulse phases in the first pseudo-continuous pulse chain are modulated alternately at 0° and 180°, and a first triangular gradient sequence with alternating reverse amplitudes is applied at the same time; the triangular gradients in the first triangular gradient sequence are synchronously applied in a one-to-one correspondence with the RF pulses in the first pseudo-continuous pulse chain, the duration of each triangular gradient is equal to the period of the RF pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative and the gradient amplitudes are different, and the average gradient of the first triangular gradient sequence is not 0.

[0045] It should be noted that the first pseudo-continuous pulse chain is composed of a series of identical RF pulses, the center distance between two adjacent RF pulses is the period of the RF pulse, and the duration between the start time and the end time of the RF pulse envelope is the duration of the RF pulse. The first triangular gradient sequence is also composed of a series of triangular gradients with equal time intervals, the center distance between two adjacent triangular gradients is the period of the triangular gradient, and the duration between the start time and the end time of the triangular gradient is the duration of the triangular gradient. In the first triangular gradient sequence, two triangular gradients are used as a repeating unit, which is repeated continuously. The triangular gradients in the first triangular gradient sequence and the RF pulses in the first pseudo-continuous pulse chain need to be applied synchronously in a one-to-one correspondence, that is, the center time of a group of corresponding triangular gradients and RF pulses coincides. It can be seen that the triangular gradients in the first triangular gradient sequence are designed in pairs, and a pair of triangular gradients completely covers two RF pulse periods, which have amplitudes in different directions and different gradient amplitudes. Therefore, the average gradient of the first triangular gradient sequence can be adjusted by changing the difference in the gradient amplitudes of two adjacent triangular gradients. The larger the difference, the larger the average gradient.

[0046] It should also be noted that the phase of the RF pulses in the first pseudo-continuous pulse chain needs to be modulated alternately at 0° and 180°, that is, the phase of the nth RF pulse is 0°, and the phases of the n+1th, n+2nd, and n+3rd RF pulses are 180°, 0°, and 180°, respectively, and so on. However, the phase of the RF pulse is relative, and the phase of the first RF pulse in the first pseudo-continuous pulse chain can be defined as 0°, and then the phases of subsequent RF pulses can be controlled to change alternately.

[0047] Continue to see Figure 4 As shown in the control part in , in the control period of the silent pCASL sequence, a second pseudo-continuous pulse chain is applied which has the same parameters as the first pseudo-continuous pulse chain except the phase, and the phase of the RF pulse in the first pseudo-continuous pulse chain is constant at 0°, and a second alternating reverse triangle gradient sequence is applied at the same time; the triangle gradients in the second triangle gradient sequence are synchronously applied in a one-to-one correspondence with the RF pulses in the second pseudo-continuous pulse chain, the duration of each triangle gradient is equal to the period of the RF pulse, the amplitude directions of two adjacent triangle gradients are one positive and one negative and the gradient amplitudes are the same, and the average gradient of the second triangle gradient sequence is 0.

[0048] It should be noted that the RF pulses in the second pseudo-continuous pulse chain and the RF pulses in the first pseudo-continuous pulse chain are only different in phase, but the pulse duration, period, amplitude and other parameters other than the phase are the same. The phase of the RF pulses in the first pseudo-continuous pulse chain needs to be modulated alternately at 0° and 180°, but the phase of the RF pulses in the second pseudo-continuous pulse chain can always be kept at 0°. In addition, the difference between the triangular gradient in the second triangular gradient sequence and the triangular gradient in the first triangular gradient sequence is only the difference in the average gradient value. The average gradient of the first triangular gradient sequence needs to be non-0, while the average gradient in the second triangular gradient sequence needs to be 0, so that the amplitude directions of the two adjacent triangular gradients in the second triangular gradient sequence are one positive and one negative and the gradient amplitude needs to be exactly the same.

[0049] In addition, in the above Figure 4 In the silent pCASL sequence shown, a triangular gradient is used in the marking period to replace the traditional layer-selected trapezoidal gradient, and also replaces the triangular re-convergence gradient, and the average gradient required for the blood flow reversal condition is achieved by the difference between the paired triangular gradients with positive and negative amplitudes. Similarly, in the control period, a triangular gradient is also used to replace the trapezoidal gradient and the triangular gradient in the traditional practice. The non-re-convergence gradient used in the silent pCASL sequence of the present invention can greatly reduce the acoustic noise of the pCASL sequence in the marking part, and the specific noise reduction effect will be demonstrated later through specific embodiments.

[0050] In addition, based on the same inventive concept, the present invention also provides a magnetic resonance arterial blood flow silent marking system, such as Figure 5 As shown, it includes a marking cycle module and a control cycle module which are executed alternately during the scanning process;

[0051] The marking period module is used to apply a first pseudo-continuous pulse chain consisting of a series of radio frequency pulses with equal time intervals to mark the spin protons in arterial blood during the marking period, and the radio frequency pulse phases in the first pseudo-continuous pulse chain are alternately modulated at 0° and 180°, and a first triangular gradient sequence with alternating reverse amplitudes is applied at the same time; the triangular gradients in the first triangular gradient sequence are synchronously applied in a one-to-one correspondence with the radio frequency pulses in the first pseudo-continuous pulse chain, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative and the gradient amplitudes are different, and the average gradient of the first triangular gradient sequence is not 0;

[0052] The control cycle module is used to apply a second pseudo-continuous pulse chain in the control cycle, which has the same parameters as the first pseudo-continuous pulse chain except the phase, and the phase of the radio frequency pulse in the first pseudo-continuous pulse chain is constant at 0°, and at the same time apply a second triangular gradient sequence that is alternating in the opposite direction; the triangular gradients in the second triangular gradient sequence are synchronously applied in a one-to-one correspondence with the radio frequency pulses in the second pseudo-continuous pulse chain, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative and the gradient amplitudes are the same, and the average gradient of the second triangular gradient sequence is 0.

[0053] It should be noted that the above-mentioned marking cycle module and control cycle module are actually completely corresponding to the specific practices in the above-mentioned magnetic resonance arterial blood flow silent marking method, so the specific implementation and requirements within each module will not be repeated.

[0054] In addition, the control parameters of various radio frequency pulses and gradients in the silent pCASL sequence can be optimized according to actual effects.

[0055] In another embodiment of the present invention, a parameter optimization method is also provided for the magnetic resonance arterial blood flow silent marking system in the above embodiment, which specifically includes:

[0056] S1. For the marking period module, the period of the radio frequency pulse in the first pseudo-continuous pulse chain, the radio frequency pulse intensity, the duration of a single radio frequency pulse, and the positive gradient amplitude, negative gradient amplitude, and duration of a single triangle gradient of two adjacent triangle gradients in the first triangle gradient sequence are used as the first optimization parameter combination. For each feasible solution of the first optimization parameter combination in the solution space, the signal value of the hydrogen atoms on the water molecules in the arterial blood flow is calculated by numerical simulation, and the negative maximization of the signal value is taken as the goal to obtain the optimal solution of the first optimization parameter combination and use it as the radio frequency pulse and triangle gradient parameters in the marking period module;

[0057] S2. For the control period module, the period of the RF pulse in the second pseudo-continuous pulse chain, the RF pulse intensity, the duration of a single RF pulse, and the positive gradient amplitude, negative gradient amplitude, and duration of a single triangular gradient of two adjacent triangular gradients in the second triangular gradient sequence are used as the second optimization parameter combination. For each set of feasible solutions of the second optimization parameter combination in the solution space, the signal values ​​of hydrogen atoms on water molecules in the arterial blood flow are calculated through numerical simulation. With the goal of maximizing the positive direction of the signal value, the optimal solution of the second optimization parameter combination is obtained and used as the RF pulse and triangular gradient parameters in the control period module.

[0058] It should be noted that the solution space of the first optimization parameter combination and the second optimization parameter combination is composed of the value ranges of all the parameters to be optimized. By sampling each parameter to be optimized within its value range, a set of feasible solutions can be formed. However, when sampling to obtain a feasible solution, it is necessary to meet the constraints on the RF pulse and the triangular gradient within the cycle. For example, the positive gradient amplitude and negative gradient amplitude of two adjacent triangular gradients in the marking cycle are not allowed to be the same, while the positive gradient amplitude and negative gradient amplitude of two adjacent triangular gradients in the control cycle must be the same. For another example, in the marking cycle and the control cycle, the duration of each triangular gradient must be equal to the period of the RF pulse.

[0059] In the present invention, for each feasible solution of the first optimization parameter combination and the second optimization parameter combination in the solution space, it is necessary to calculate the signal value of the hydrogen atoms on the water molecules in the arterial blood flow by numerical simulation. The specific numerical simulation process can be implemented by referring to the prior art.

[0060] In an embodiment of the present invention, a numerical simulation method of hard pulse approximation can be used, and the specific method is as follows: first, according to the type of the current simulated cycle (marking cycle or control cycle), a pseudo-continuous pulse chain and a triangular gradient sequence in the corresponding cycle module are constructed based on the currently selected feasible solution (a first pseudo-continuous pulse chain and a first triangular gradient sequence in the marking cycle, and a second pseudo-continuous pulse chain and a second triangular gradient sequence in the control cycle), and then the time domain range of the sequence is discretized, so that the envelope shape of each RF pulse in the pseudo-continuous pulse chain and each triangular gradient in the triangular gradient sequence is discretized according to a fixed time step. Divide into rectangular regions (similar to the approximate algorithm for integral calculation), time step length It is generally set to a few microseconds, and each time step is regarded as a hard pulse, corresponding to an RF pulse intensity and gradient value. Then, the hard pulses are simulated and calculated one by one in sequence, and the magnetic field amplitude of the gradient field at the target spatial position is calculated according to the corresponding gradient value at each time step, and then the final equivalent magnetic field is synthesized with the RF magnetic field corresponding to the hard pulse. The equivalent magnetic field amplitude is then used to calculate the reversal angle of the hydrogen atoms in three-dimensional space, and the attenuation of the longitudinal and transverse components of the signal during this rectangular time is considered at the same time, so as to obtain the final signal value of the hydrogen atoms on the water molecules in the blood flow at the target spatial position.

[0061] Specifically, assuming that for the hard pulse of the current time step to be calculated, the signal of the hydrogen atoms on the water molecules in the blood flow at the target spatial position before the hard pulse is applied is M, then the magnetic field amplitude of the gradient field at the target spatial position is calculated using the gradient value of the current time step and the spatial position coordinates of the target, and then synthesized with the radio frequency magnetic field to form the final equivalent magnetic field , the calculation formula is as follows:

[0062]

[0063] in is the magnetic field strength of the RF pulse at the current time step, is the gradient value and the gradient amplitude of the current time step, is the spatial position of the excitation target relative to the center of the main magnetic field.

[0064] Through the equivalent magnetic field The rotational angular velocity w of the hydrogen atom in the magnetic field can be calculated as follows:

[0065]

[0066] in is the magnetic gyrometry ratio of the hydrogen atom, which is 42.576 MHz / T.

[0067] Based on the angular velocity and duration t, the flip angle can be calculated =wt.

[0068] The position of the magnetic vector after the equivalent magnetic field is flipped can be calculated by the rotation matrix and described in the rotating coordinate system. The situation where the hydrogen atom rotates along the three axes of x, y, and z can be expressed as:

[0069]

[0070]

[0071]

[0072] The process of hydrogen atom rotation is to first transform the coordinates and then convert them into equivalent magnetic field. Flip the angle and restore the coordinates. The specific processing process is as follows: Equivalent magnetic field Positions in three-dimensional space are given by polar angles and azimuth Indicates that the signal M of the hydrogen atom at the target spatial position is rotated by an angle equal to the equivalent magnetic field direction, and then according to the equivalent magnetic field The strength of the flip Finally, the signal M is transformed back to the previous coordinate system by reverse rotation. After this process, the signal value of the hydrogen atom on the water molecule in the blood flow at the target spatial position is finally obtained. , from M to The process is expressed by the formula:

[0073]

[0074] Where:

[0075]

[0076]

[0077]

[0078] In addition, the signal value On the basis of this, it is also necessary to consider the attenuation of the longitudinal and transverse components of the signal during this period of time. This is achieved by performing longitudinal relaxation (T1 relaxation) and transverse relaxation (T2 relaxation). and the longitudinal magnetization The final signal value of the hydrogen atoms on the water molecules in the blood flow at the target spatial position can be re-determined The specific method of T1 relaxation and T2 relaxation belongs to the prior art, and the calculation process can be expressed as:

[0079]

[0080]

[0081] Where: Initial magnetization in thermal equilibrium; is the time step, T1 is the longitudinal relaxation time, and T2 is the transverse relaxation time; is the signal value The initial transverse magnetization intensity, is the signal value The initial longitudinal magnetization.

[0082] When calculated by M After that, the simulation calculation of a hard pulse is completed. When a RF pulse of the present invention contains a series of hard pulses, it is necessary to perform iterative simulation calculations on each hard pulse. At the same time, the RF pulses in the pseudo-continuous pulse chain and the triangular gradients in the triangular gradient sequence are repeated continuously, so the simulation calculations of each group of RF pulses and triangular gradients also need to be performed in sequence until all the RF pulses and triangular gradients of the entire sequence are calculated. Generally speaking, a single RF pulse requires the simulation results of about several hundred hard pulses to be superimposed, and the signal of the entire cycle process requires the simulation results of several thousand RF pulses to be superimposed, so a marking cycle or a control cycle requires a total of about one million hard pulse simulations.

[0083] The final signal value of hydrogen atoms in three-dimensional space in the simulation results As a design goal, the signal value in the marking cycle It needs to be a negative number, and the larger the amplitude, the better the effect. However, in the control period, the signal value It needs to be a positive number, and the larger the amplitude, the better the effect. In the embodiment of the present invention, the optimization target is set as the final signal value of the hydrogen atoms on the water molecules in the blood flow at the target spatial position in the marking cycle. As close to -1 as possible, while the optimization target in the control cycle is set to the final signal value of the hydrogen atoms on the water molecules in the blood flow at the target spatial position +1 for as close as you can get.

[0084] In a preferred embodiment of the present invention, a set of optimal parameters (referred to as the "optimal parameter group" for the convenience of subsequent description) obtained through the above optimization are as follows: in the first triangular gradient sequence, the gradient amplitudes of two adjacent triangular gradients are 8 mT / m and -6 mT / m, respectively, and the average gradient is 0.5 mT / m. In the second triangular gradient sequence, the gradient amplitudes of two adjacent triangular gradients are 8 mT / m and -8 mT / m, respectively, and the average gradient is 0 mT / m. The period of the RF pulses in the first pseudo-continuous pulse chain and the second pseudo-continuous pulse chain are both 1000 µs, the duration of a single RF pulse is both 500 µs, and the average intensity of the RF pulse is 1.7uT; the duration of the triangular gradients in the first triangular gradient sequence and the second triangular gradient sequence is both 1000 µs. Therefore, the silent pCASL sequence under this "optimal parameter group" is as follows: Figure 6 shown.

[0085] In another embodiment of the present invention, an arterial spin labeling imaging method is also provided, which is in accordance with the magnetic resonance arterial blood flow silent labeling method in the above embodiment, alternately performs labeling cycles and control cycles during the scanning process, and waits for the labeled blood to flow into the imaging area after each labeling cycle (the waiting time can be recorded as the post-labeling delay PLD) and collects the labeled image, and waits for the labeled blood to flow into the imaging area after each control cycle and collects the reference image. After obtaining the labeled image and the reference image, the specific image post-processing can be selected according to actual clinical needs. Generally speaking, the signal intensity of the labeled image is subtracted from the signal intensity of the reference image to obtain a signal difference, and this signal difference reflects the arterial blood flow condition flowing into the imaging area during the labeling cycle. In addition, based on the signal difference, an arterial blood flow perfusion map can be generated, and various analyses can be carried out based on the perfusion map, such as calculating the average blood flow, blood flow peak and other parameters of a specific area (such as brain tissue, tumor, etc.).

[0086] The above-mentioned magnetic resonance arterial blood flow silent marking method is applied to a specific example below to demonstrate the technical effect that can be achieved.

[0087] Example

[0088] In this embodiment, according to the above-mentioned magnetic resonance arterial blood flow silent marking method, the above-mentioned Figure 4 The silent pCASL sequence shown was implemented and tested on a Siemens 3T Prisma scanner (Siemens Healthcare, Erlangen, Germany). The parameters in the sequence were set according to the "optimal parameter set" obtained by the above optimization. The specific experimental process and results are shown below.

[0089] The labeling efficiency was simulated by labeling duration = 2s, average B1 = 1.7uT, blood flow velocity = 35cm / m, T1 = 1650ms and T2 = 250ms at a frequency shift from -980Hz to 980Hz. Static layer selection of gray matter was simulated with T1 = 1331ms and T2 = 80ms.

[0090] The non-resonant frequency ranged from -500 Hz to 500 Hz with a step length of 40 Hz. Five healthy subjects were scanned. The average signal in the gray matter was calculated as an indicator of labeling efficiency. The experimental parameters were set as follows: The FOV of the ASL image acquisition was , WASPI acquisition part, the parameter leaf number (interleave) of the outer part is 8, the number of spokes per leaf is 101, the interleave of the inner part is 1, and the number of spokes per leaf is 160. The resolution is , the post-marking delay (PLD) is 1180ms, and it takes 47.6 minutes.

[0091] The final result is Figure 7 As shown in Figure a), it can be seen that the labeling plane of the proposed blood flow labeling method is located outside the imaging brain area and will not interfere with the imaging process. Figure 7 The simulation results shown in b) and the experimental test results shown in c) are consistent, indicating that the blood flow marker has a higher marking efficiency in the range of about 100 Hz near the resonance frequency. This result can also be directly observed and verified in the human body test image in d), that is, the image signal near the center frequency is stronger.

[0092] In addition, the noise of the silent pCASL sequence of the present invention and the traditional pCASL in the blood flow labeling process were tested successively on the Siemens machine. The noise test results are as follows: Figure 8 As shown, the calculation results show that the silent pCASL sequence of the present invention ( Figure 8 The noise in part A of Figure 3 The traditional pCASL sequence ( Figure 8 of Section B).

[0093] In addition, the quality of the final blood perfusion images obtained on multiple subjects was compared. Fig. 9 As shown, it is demonstrated that the present invention can improve image quality.

[0094] It should be noted that the methods and system steps shown in the above embodiments can essentially be implemented in the form of computer programs.

[0095] Therefore, based on the same inventive concept, Fig.10As shown, the present invention also provides a computer electronic device corresponding to the magnetic resonance arterial blood flow silent marking method provided in the above embodiment, which includes a memory and a processor;

[0096] The memory is used to store computer programs;

[0097] The processor is used to implement the magnetic resonance arterial blood flow silent marking method as described above when executing the computer program;

[0098] In addition, the logic instructions in the above-mentioned memory can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on such an understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention.

[0099] Therefore, based on the same inventive concept, the present invention provides a computer-readable storage medium corresponding to a magnetic resonance arterial blood flow silent marking method, on which a computer program is stored. When the computer program is executed by a processor, the magnetic resonance arterial blood flow silent marking method as described above can be implemented.

[0100] Therefore, based on the same inventive concept, the present invention provides a computer program product, including a computer program / instruction, which, when executed by a processor, can implement the magnetic resonance arterial blood flow silent marking method as described above.

[0101] It is understandable that the above storage medium may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage. The storage medium may also be a U disk, a mobile hard disk, a magnetic disk or an optical disk, etc., which can store program codes.

[0102] It is understandable that the above-mentioned processor can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.

[0103] It should also be noted that those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process of the system described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. In the various embodiments provided in this application, the division of steps or modules in the system and method is only a logical function division, and there may be other division methods in actual implementation, such as multiple modules or steps can be combined or integrated together, and a module or step can also be split.

[0104] The above-described embodiments are only some preferred implementations of the present invention, but are not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A magnetic resonance arterial blood flow silent marking method, characterized in that: Labeling cycles and control cycles were performed alternately during the scan; In the labeling period, a first pseudo-continuous pulse train consisting of a series of radio frequency pulses with equal time intervals is applied to label the spinning protons in the arterial blood, and the radio frequency pulse phases in the first pseudo-continuous pulse train are alternately modulated at 0° and 180°, and a first triangular gradient sequence with alternating reverse amplitudes is applied simultaneously; The triangular gradients in the first triangular gradient sequence are synchronously applied in one-to-one correspondence with the radio frequency pulses in the first pseudo-continuous pulse chain, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative, and the gradient amplitudes are different, and the average gradient of the first triangular gradient sequence is not 0; In the control period, a second pseudo-continuous pulse chain is applied, which has the same parameters as the first pseudo-continuous pulse chain except the phase, and the phase of the radio frequency pulse in the first pseudo-continuous pulse chain is constant at 0°, and a second triangular gradient sequence is applied in an alternating reverse direction; the triangular gradients in the second triangular gradient sequence are applied synchronously with the radio frequency pulses in the second pseudo-continuous pulse chain in a one-to-one correspondence, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative, and the gradient amplitudes are the same, and the average gradient of the second triangular gradient sequence is 0.

2. The magnetic resonance arterial blood flow silent marking method according to claim 1, characterized in that: In the first triangle gradient sequence, the gradient amplitudes of two adjacent triangle gradients are 8 mT / m and -6 mT / m respectively, and the average gradient is 0.5 mT / m.

3. The magnetic resonance arterial blood flow silent marking method according to claim 1, characterized in that: In the second triangle gradient sequence, the gradient amplitudes of two adjacent triangle gradients are 8 mT / m and -8 mT / m respectively, and the average gradient is 0 mT / m.

4. The magnetic resonance arterial blood flow silent marking method according to claim 1, characterized in that: The period of the radio frequency pulses in the first pseudo-continuous pulse chain and the second pseudo-continuous pulse chain is 1000 µs, the duration of a single radio frequency pulse is 500 µs, and the average intensity of the radio frequency pulse is 1.7uT; the duration of the triangular gradient in the first triangular gradient sequence and the second triangular gradient sequence is 1000 µs.

5. A magnetic resonance arterial blood flow silent marking system, characterized in that: It includes a marking cycle module and a control cycle module which are executed alternately during the scanning process; The labeling period module is used to apply a first pseudo-continuous pulse chain consisting of a series of radio frequency pulses with equal time intervals to label the spin protons in the arterial blood during the labeling period, and the radio frequency pulse phases in the first pseudo-continuous pulse chain are alternately modulated at 0° and 180°, and a first triangular gradient sequence with alternating reverse amplitudes is applied at the same time; The triangular gradients in the first triangular gradient sequence are synchronously applied in one-to-one correspondence with the radio frequency pulses in the first pseudo-continuous pulse chain, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative, and the gradient amplitudes are different, and the average gradient of the first triangular gradient sequence is not 0; The control cycle module is used to apply a second pseudo-continuous pulse chain in the control cycle, which has the same parameters as the first pseudo-continuous pulse chain except the phase, and the phase of the radio frequency pulse in the first pseudo-continuous pulse chain is constant at 0°, and at the same time apply a second triangular gradient sequence that is alternating in the opposite direction; the triangular gradients in the second triangular gradient sequence are synchronously applied in a one-to-one correspondence with the radio frequency pulses in the second pseudo-continuous pulse chain, the duration of each triangular gradient is equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients are one positive and one negative and the gradient amplitudes are the same, and the average gradient of the second triangular gradient sequence is 0.

6. A parameter optimization method for the magnetic resonance arterial blood flow silent marking system as claimed in claim 5, characterized in that: include: S1. For the marking period module, the period of the radio frequency pulse in the first pseudo-continuous pulse chain, the radio frequency pulse intensity, the duration of a single radio frequency pulse, and the positive gradient amplitude, negative gradient amplitude, and duration of a single triangle gradient of two adjacent triangle gradients in the first triangle gradient sequence are used as the first optimization parameter combination. For each feasible solution of the first optimization parameter combination in the solution space, the signal value of the hydrogen atoms on the water molecules in the arterial blood flow is calculated by numerical simulation, and the negative maximization of the signal value is taken as the goal to obtain the optimal solution of the first optimization parameter combination and use it as the radio frequency pulse and triangle gradient parameters in the marking period module; S2. For the control period module, the period of the RF pulse in the second pseudo-continuous pulse chain, the RF pulse intensity, the duration of a single RF pulse, and the positive gradient amplitude, negative gradient amplitude, and duration of a single triangular gradient of two adjacent triangular gradients in the second triangular gradient sequence are used as the second optimization parameter combination. For each set of feasible solutions of the second optimization parameter combination in the solution space, the signal values ​​of hydrogen atoms on water molecules in the arterial blood flow are calculated through numerical simulation. With the goal of maximizing the positive direction of the signal value, the optimal solution of the second optimization parameter combination is obtained and used as the RF pulse and triangular gradient parameters in the control period module.

7. An arterial spin labeling imaging method, characterized in that: According to the magnetic resonance arterial blood flow silent marking method as described in any one of claims 1 to 4, marking cycles and control cycles are performed alternately during the scanning process, and after each marking cycle, the marked blood is waited to flow into the imaging area and the marked image is collected, and after each control cycle, the marked blood is waited to flow into the imaging area and the reference image is collected.

8. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the magnetic resonance arterial blood flow silent marking method as described in any one of claims 1 to 4 can be implemented.

9. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by a processor, the magnetic resonance arterial blood flow silent marking method as described in any one of claims 1 to 4 can be implemented.

10. A computer electronic device, characterized in that: including memory and processor; The memory is used to store computer programs; The processor is used to implement the magnetic resonance arterial blood flow silent marking method as described in any one of claims 1 to 4 when executing the computer program.

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