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

Abstract

The present invention discloses a method, system, medium and electronic equipment for silent marking of magnetic resonance arterial blood flow, which belongs to the field of magnetic resonance technology. In the marking cycle, the present invention uses a triangular gradient to replace the traditional layer-selected trapezoidal gradient, and also replaces the triangular reconvergence gradient, and the average gradient required for the blood flow reversal condition is achieved by the difference between 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 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-reconvergence gradient to achieve magnetic resonance arterial blood flow marking, which can greatly reduce the acoustic noise of blood flow marking.

Description

Technical Field

[0001] The present 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), a noninvasive magnetic resonance perfusion imaging method, has been widely used in clinical practice and scientific research. Its basic principle is to use water molecules in the arteries as endogenous tracers, inverting the magnetic resonance signal of the water molecules through radiofrequency pulses, and then tracking the flow of water molecules. When water molecules with an inverted signal flow into human tissue (such as the gray matter of the brain), they partially offset the signal of water molecules in the tissue, thereby reducing the overall signal of the tissue. By calculating the change in signal, the amount of water molecules exchanged can be determined, and thus the blood perfusion status, 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 direction (along the main magnetic field direction) and the reverse direction (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 vectorial 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 technology (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 RF power amplifier), and each switching cycle However, the gradient magnetic field needs to increase the current to generate the magnetic field when it changes, and it will also generate noise, especially when the gradient field changes rapidly (corresponding to Figure 2The rising and falling edges of the green trapezoids and triangles in the middle generate strong noise, which increases with faster gradient transition rates. This can be uncomfortable for patients and may introduce interference signals during resting-state functional brain imaging. In accordance with international guidelines for arterial spin labeling imaging, the flow inversion design uses ultrashort gradients (approximately 500 μs each) at maximum transition rates, including trapezoids (for labeling plane selection) and triangles (for signal refocusing). This generates strong noise.

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

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

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

[0008] In a first aspect, the present invention provides a method for silent marking of magnetic resonance arterial blood flow, wherein a marking period and a control period are alternately performed during a scan;

[0009] During a labeling period, a first pseudo-continuous pulse train consisting of a series of radiofrequency pulses with equal time intervals is applied to label spinning protons in arterial blood, wherein the phases of the radiofrequency pulses in the first pseudo-continuous pulse train are alternately modulated between 0° and 180°, and a first triangular gradient sequence with alternating opposite amplitudes is simultaneously applied; the triangular gradients in the first triangular gradient sequence are synchronously applied in a one-to-one correspondence with the radiofrequency pulses in the first pseudo-continuous pulse train, the duration of each triangular gradient is equal to the period of the radiofrequency 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 zero;

[0010] In the control period, a second pseudo-continuous pulse chain was applied with the same parameters as the first pseudo-continuous pulse chain except for the phase, and the phase of the radio frequency pulses in the second pseudo-continuous pulse chain was constant at 0°. At the same time, a second triangular gradient sequence with alternating opposite directions was applied; the triangular gradients in the second triangular gradient sequence were 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 was equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients were one positive and one negative, and the gradient amplitudes were the same, and the average gradient of the second triangular gradient sequence was 0.

[0011] As a preference for the first aspect above, 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 1.7 uT; the duration of the triangular gradient in the first triangular gradient sequence and the second triangular gradient sequence is 1000 µs.

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

[0015] The labeling period module is configured to apply a first pseudo-continuous pulse train consisting of a series of radio frequency pulses with equal time intervals to label spinning protons in arterial blood during the labeling period, wherein the phases of the radio frequency pulses in the first pseudo-continuous pulse train are alternately modulated at 0° and 180°, and a first triangular gradient sequence with alternating opposite amplitudes is applied simultaneously; the triangular gradients in the first triangular gradient sequence are applied synchronously with the radio frequency pulses in the first pseudo-continuous pulse train 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 different, and the average gradient of the first triangular gradient sequence is not zero;

[0016] The control period module is used to apply, during the control period, a second pseudo-continuous pulse chain having the same parameters as the first pseudo-continuous pulse chain except for the phase, and the phase of the radio frequency pulses in the second pseudo-continuous pulse chain is constant at 0°, and simultaneously apply a second triangular gradient sequence that alternates in opposite directions; the triangular gradients in the second triangular gradient sequence are applied synchronously 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 a 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 through numerical simulation. With the goal of maximizing the negative direction of the signal value, the optimal solution of the first optimization parameter combination is obtained and used 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 the 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 a scan 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, comprising 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 solutions in 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 configured 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] During the labeling cycle, the present invention uses triangular gradients instead of traditional slice-selective trapezoidal gradients, also replacing triangular reconverging gradients. The average gradient required for the blood flow reversal condition is achieved by the difference between pairs of triangular gradients with positive and negative amplitudes. Similarly, during the control cycle, triangular gradients replace the traditional trapezoidal and triangular gradients, but the average gradient of the triangular gradient sequence is controlled to zero. The present invention uses non-reconverging gradients to achieve MRI arterial blood flow labeling, significantly reducing the acoustic noise of the blood flow labeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 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 radiofrequency pulses and gradients for the labeled and control parts of the pCASL sequence;

[0031] Figure 4 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 following are the results of different links in the embodiment of the present invention, where a) is the layer selection mark plane, b) is the result of non-resonant frequency simulation, c) is the average signal curve of 5 subjects, and d) is the human body test result of non-resonant frequency test;

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

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

[0037] Figure 10 A schematic diagram of the composition of computer electronic equipment. DETAILED DESCRIPTION

[0038] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0039] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to 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 than 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 the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0040] In the description of the present invention, it should be understood that when an element is considered to be "connected" to another element, it can 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 used solely for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly specifying the number of technical features being described. Therefore, features defined as "first" or "second" may explicitly or implicitly include at least one of such 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), a positive trapezoidal gradient for marker plane selection and a negative triangular gradient (red) for signal refocusing are individually designed. In other words, both a trapezoidal gradient and a triangular gradient are applied within a single RF pulse cycle. However, due to the maximum gradient transition rate used for blood flow inversion, this sequence can generate significant noise in practical applications. The faster the gradient transition 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 requires alternating label and control cycles during scanning, but the specific pulse and gradient forms in the label and control cycles are different.

[0044] Continue to see Figure 4 As shown in the marked portion in , during the labeling 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 label 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°, while a first triangular gradient sequence with alternating reverse amplitudes is applied simultaneously; the triangular gradients in the first triangular gradient sequence are applied synchronously with the RF pulses in the first pseudo-continuous pulse chain in a one-to-one correspondence, 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 zero.

[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 RF pulse period, and the duration between the start and end times of the RF pulse envelope is the RF pulse duration. 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 triangular gradient period, and the duration between the start and end times of the triangular gradient is the triangular gradient duration. 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 times of a set of corresponding triangular gradients and RF pulses coincide. 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. They 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 RF pulse phases in the first pseudo-continuous pulse train need to be modulated alternately between 0° and 180°. That is, if the phase of the nth RF pulse is 0°, then the phases of the n+1th, n+2th, and n+3th RF pulses are 180°, 0°, 180°, and so on. However, the phases of RF pulses are relative. The first RF pulse in the first pseudo-continuous pulse train can be defined as 0°, and the phases of subsequent RF pulses can then be controlled to alternate.

[0047] Continue to see Figure 4 As shown in the control portion of FIG, during the control period of the silent pCASL sequence, a second pseudo-continuous pulse chain having the same parameters as the first pseudo-continuous pulse chain except for the phase is applied, and the phase of the RF pulses in the second pseudo-continuous pulse chain is constant at 0°. Simultaneously, a second alternating and reversed triangular gradient sequence is applied; the triangular gradients in the second triangular gradient sequence are applied synchronously with the RF 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 RF 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.

[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 RF pulse phase in the first pseudo-continuous pulse chain needs to be modulated alternately at 0° and 180°, but the RF pulse phase 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 average gradient value. The average gradient of the first triangular gradient sequence needs to be non-zero, while the average gradient in the second triangular gradient sequence needs to be zero. Therefore, the amplitude directions of the two adjacent triangular gradients in the second triangular gradient sequence are one positive and one negative, and the gradient amplitudes need to be exactly the same.

[0049] In addition, in the above Figure 4 In the silent pCASL sequence shown, a triangular gradient replaces the traditional layer-selective trapezoidal gradient during the marking period, also replacing the triangular reconverging gradient. The average gradient required for the blood flow reversal condition is achieved by the difference between pairs of triangular gradients with positive and negative amplitudes. Similarly, a triangular gradient replaces the traditional trapezoidal and triangular gradients during the control period. The non-reconverging gradient used in the silent pCASL sequence of the present invention can significantly reduce the acoustic noise of the pCASL sequence during the marking portion. The specific noise reduction effect will be demonstrated later through specific examples.

[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 labeling period module is configured to apply a first pseudo-continuous pulse train consisting of a series of radio frequency pulses with equal time intervals to label spinning protons in arterial blood during the labeling period, wherein the phases of the radio frequency pulses in the first pseudo-continuous pulse train are alternately modulated at 0° and 180°, and a first triangular gradient sequence with alternating opposite amplitudes is applied simultaneously; the triangular gradients in the first triangular gradient sequence are applied synchronously with the radio frequency pulses in the first pseudo-continuous pulse train 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 different, and the average gradient of the first triangular gradient sequence is not zero;

[0052] The control period module is used to apply, during the control period, a second pseudo-continuous pulse chain having the same parameters as the first pseudo-continuous pulse chain except for the phase, and the phase of the radio frequency pulses in the second pseudo-continuous pulse chain is constant at 0°, and simultaneously apply a second triangular gradient sequence that alternates in opposite directions; the triangular gradients in the second triangular gradient sequence are applied synchronously 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 are not repeated here.

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

[0055] In another embodiment of the present invention, a parameter optimization method is 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 a 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 through numerical simulation. With the goal of maximizing the negative direction of the signal value, the optimal solution of the first optimization parameter combination is obtained and used 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 the 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 each 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 period are not allowed to be the same, while the positive gradient amplitude and negative gradient amplitude of two adjacent triangular gradients in the control period must be the same. For another example, in the marking period and the control period, 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 in the solution space for the first and second optimization parameter combinations, the signal values of hydrogen atoms attached to water molecules in the arterial blood flow need to be calculated through numerical simulation. The specific numerical simulation process can be implemented with reference to existing technologies.

[0060] In an embodiment of the present invention, a numerical simulation method of hard pulse approximation can be used, specifically as follows: first, according to the type of cycle currently simulated (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 (the first pseudo-continuous pulse chain and the first triangular gradient sequence in the marking cycle, and the second pseudo-continuous pulse chain and the 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 areas (similar to the approximate algorithm for integral calculation), time step length Typically set at a few microseconds, each time step is considered a hard pulse, corresponding to a specific RF pulse intensity and gradient value. Simulation calculations are then performed sequentially for each hard pulse. At each time step, the magnetic field amplitude of the gradient field at the target spatial location is calculated based on the corresponding gradient value. This is then combined with the RF magnetic field corresponding to the hard pulse to form the final equivalent magnetic field. The equivalent magnetic field amplitude is then used to calculate the reversal angle of the hydrogen atoms in three-dimensional space, while also considering the attenuation of the longitudinal and transverse components of the signal during this rectangular time period. This yields the final signal value of the hydrogen atoms attached to water molecules in the bloodstream at the target spatial location.

[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 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 hydrogen atoms, which is 42.576 MHz / T.

[0067] Based on the angular velocity of rotation 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 case where the hydrogen atom rotates along the x, y, and z axes alone can be expressed as:

[0069]

[0070]

[0071]

[0072] The process of hydrogen atom rotation is to first transform the coordinates and then calculate the equivalent magnetic field. Flip the angle and restore the coordinates. The specific processing process is as follows: Equivalent magnetic field Position in three-dimensional space using polar angle 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 corresponds to the equivalent magnetic field Intensity 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 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, we also need to consider the attenuation of the longitudinal and transverse components of the signal during this period of time, and the signal value can be This is achieved by performing longitudinal relaxation (T1 relaxation) and transverse relaxation (T2 relaxation), according to the attenuated transverse magnetization and 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 methods of T1 relaxation and T2 relaxation belong 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, 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 radio frequency 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 radio frequency pulses in the pseudo-continuous pulse chain and the triangular gradients in the triangular gradient sequence are continuously repeated, so the simulation calculations of each group of radio frequency pulses and triangular gradients also need to be performed in sequence until all the radio frequency pulses and triangular gradients in the entire sequence are calculated. Generally speaking, a single radio frequency pulse requires the simulation results of about hundreds of hard pulses to be superimposed, and the signal of the entire cycle process requires the simulation results of thousands of radio frequency 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 to the final signal value of the hydrogen atoms on the water molecules in the blood flow at the target spatial position during 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 bloodstream at the target spatial position +1 as close as possible.

[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 are 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 provided. Following the MRI arterial blood flow silent labeling method described in the aforementioned embodiment, labeling cycles and control cycles are alternately executed during the scanning process. After each labeling cycle, a waiting period is maintained for labeled blood to flow into the imaging region (this waiting period can be referred to as the post-labeling delay (PLD)) before acquiring a labeled image. After each control cycle, a waiting period is maintained for labeled blood to flow into the imaging region before acquiring a reference image. After acquiring the labeled and reference images, specific image post-processing can be selected based on actual clinical needs. Generally, the signal intensity of the reference image is subtracted from the signal intensity of the labeled image to obtain a signal difference. This signal difference reflects the arterial blood flow in the imaging region during the labeling cycle. Furthermore, based on this signal difference, an arterial blood perfusion map can be generated. This perfusion map can be used to perform various analyses, such as calculating parameters such as average blood flow and peak blood flow in specific regions (e.g., brain tissue or tumors).

[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 sequence parameters were set according to the "optimal parameter set" obtained through the optimization described above. The detailed experimental procedures and results are presented below.

[0089] The labeling efficiency was simulated with 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 slice selection of gray matter was simulated with T1 = 1331ms and T2 = 80ms.

[0090] The non-resonant frequency ranged from -500Hz to 500Hz with a step size of 40Hz. Five healthy subjects were scanned. The average signal within 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 outer part has an interleave of 8 and a spoke number of 101, the inner part has an interleave of 1 and a spoke number of 160. The resolution is , the post-marking delay (PLD) is 1180ms, and it takes 47.6 minutes.

[0091] The final result is as follows 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 blood flow labeling has a high labeling efficiency in the range of approximately 100 Hz near the resonant 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 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 Part B of the 2020 Budget for 2020-2025 was 47%.

[0093] In addition, the quality of the final blood perfusion images obtained on multiple subjects was compared. Figure 9 As shown, it is shown 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, Figure 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 configured to implement the aforementioned magnetic resonance arterial blood flow silent marking method when executing the computer program;

[0098] Furthermore, the logic instructions in the aforementioned memory can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute 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 understood that the storage medium may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Furthermore, the storage medium may be any medium capable of storing program code, such as a USB flash drive, a mobile hard drive, a magnetic disk, or an optical disk.

[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 brevity 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. In actual implementation, there may be other division methods, for example, multiple modules or steps can be combined or integrated together, and a module or step can also be split.

[0104] The embodiments described above are merely some preferred implementations of the present invention and are not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A magnetic resonance arterial blood flow silent marking method, characterized in that: Labeling and control cycles were performed alternately during the scan; During 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°, while 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 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. The average gradient of the first triangular gradient sequence is not zero. In the control period, a second pseudo-continuous pulse chain was applied with the same parameters as the first pseudo-continuous pulse chain except for the phase, and the phase of the radio frequency pulses in the second pseudo-continuous pulse chain was constant at 0°. At the same time, a second triangular gradient sequence with alternating opposite directions was applied; the triangular gradients in the second triangular gradient sequence were 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 was equal to the period of the radio frequency pulse, the amplitude directions of two adjacent triangular gradients were one positive and one negative, and the gradient amplitudes were the same, and the average gradient of the second triangular gradient sequence was 0.

2. The magnetic resonance arterial blood flow silent marking method according to claim 1, wherein: 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, wherein: 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, wherein: 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 1.7 uT; 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: including a marking cycle module and a control cycle module which are executed alternately during the scanning process; The labeling period module is configured to apply a first pseudo-continuous pulse train consisting of a series of radio frequency pulses with equal time intervals to label the spinning protons in arterial blood during the labeling period, wherein 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 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. The average gradient of the first triangular gradient sequence is not zero. The control period module is used to apply, during the control period, a second pseudo-continuous pulse chain having the same parameters as the first pseudo-continuous pulse chain except for the phase, and the phase of the radio frequency pulses in the second pseudo-continuous pulse chain is constant at 0°, and simultaneously apply a second triangular gradient sequence that alternates in opposite directions; the triangular gradients in the second triangular gradient sequence are applied synchronously 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 according to 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 a 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 through numerical simulation. With the goal of maximizing the negative direction of the signal value, the optimal solution of the first optimization parameter combination is obtained and used 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 the 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 for to flow into the imaging area and the marked image is acquired, and after each control cycle, the marked blood is waited for to flow into the imaging area and the reference image is acquired.

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 according to 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 according to 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 configured to implement the magnetic resonance arterial blood flow silent marking method according to any one of claims 1 to 4 when executing the computer program.

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