High-field magnetic resonance imaging methods

Abstract

This invention relates to a high-field magnetic resonance imaging (MRI) method, which uses an imaging sequence with excitation and retraction pulses for MRI. A radio frequency (RF) pulse is applied to the human tissue being examined in a main magnetic field, exciting the target region of the tissue. The precession frequencies of the target imaging material and interfering imaging material under the main magnetic field are obtained in advance, and the retraction pulse frequency parameters for non-retraction of the interfering imaging material are determined based on the two obtained precession frequencies. MRI is then performed using the imaging sequence with the determined parameters. By using the first precession frequency of the target imaging material under the main magnetic field strength as the center frequency of the retraction pulse, the target imaging interference signal is suppressed. This achieves reasonable suppression of the MRI signal of the interfering imaging material without the need for additional pulses, overcoming the problems of traditional signal suppression being sensitive to the RF field and poor imaging results caused by RF field inhomogeneity.

Description

Technical Field

[0001] This invention relates to a magnetic resonance technique, and more particularly to a high-field magnetic resonance imaging method. Background Technology

[0002] In magnetic resonance spectroscopy (MRS) imaging, especially fast spin echo imaging and echo-plane imaging with a high relaxation time (T2) weight, the strong fat signal in some tissues may mask lesions. Therefore, uniform fat suppression becomes crucial in such scenarios. Traditional fat saturation techniques utilize frequency-selective pulses to saturate the fat signal, followed by a dephasing gradient to dephasing the signal before imaging. However, the flip angle of the saturation pulse is affected by the radio frequency (RF) field, leading to poor RF field uniformity at high fields and significantly impacting fat suppression uniformity. Various fat suppression techniques exist, including FatSat, frequency-selective adiabatic flip recovery (SPAIR), and water excitation. Spin echo imaging sequences utilize excitation pulses and reverse-polarity convergence gradients. FatSat is sensitive to RF fields, resulting in uneven fat suppression at high fields. SPAIR is time-consuming and produces high energy deposition. At high fields, the increased frequency difference between water and fat makes water excitation more difficult. In spin echo imaging sequences, excitation pulses and reverse-polarity convergence gradients can lead to signal loss and a decreased signal-to-noise ratio. Therefore, how to reasonably suppress a certain signal is a technical problem that urgently needs to be solved. Summary of the Invention

[0003] To address the issues that traditional magnetic resonance imaging (MRI) techniques require additional signal suppression pulses and are sensitive to radio frequency (RF) fields, resulting in poor imaging performance when the RF field is inhomogeneous, a high-field MRI method is proposed. This method aims to effectively suppress the MRI signals of interfering imaging materials without requiring additional pulses, thereby improving the imaging performance of MRI.

[0004] The technical solution of the present invention is: a high-field magnetic resonance imaging method, which uses an imaging sequence with excitation pulse and convergence pulse to perform magnetic resonance imaging;

[0005] First, a radio frequency pulse is applied to the human tissue being examined, which is located in the main magnetic field. The radio frequency pulse excites the target area of ​​the human tissue being examined.

[0006] Then, the precession frequencies of the target imaging material and the interfering imaging material under the main magnetic field are obtained in advance, and the re-convergence pulse frequency parameters of the non-convergence interfering imaging material are determined based on the two obtained precession frequencies.

[0007] Finally, magnetic resonance imaging was performed using an imaging sequence with defined parameters.

[0008] Furthermore, the refocusing pulse frequency parameters include the refocusing pulse center frequency and the refocusing pulse frequency bandwidth. The first precession frequency of the target imaging material under the main magnetic field strength is used as the refocusing pulse center frequency. The difference between the two precession frequencies of the target imaging material and the interfering imaging material under the main magnetic field determines the refocusing pulse frequency bandwidth, ensuring that the refocused magnetic resonance signal does not contain the magnetic resonance signal of the interfering imaging material.

[0009] Furthermore, the recoil pulse frequency bandwidth is determined by any precession frequency less than twice the difference between the two precession frequencies.

[0010] Furthermore, the imaging protons in the target imaging material and the interfering imaging material need to have different precession frequencies.

[0011] Furthermore, the target imaging substance and the interfering imaging substance are determined according to actual needs, and the target imaging substance and the interfering imaging substance are at least one of water, fat, muscle, bone, and various organ tissues, and the target imaging substance and the interfering imaging substance are different substances.

[0012] Furthermore, the target imaging material and the interfering imaging material are determined according to actual needs, and the target imaging material and the interfering imaging material are atoms with different precession frequencies in the same type of material.

[0013] Furthermore, the imaging sequence excitation pulse can be a layer-selective excitation pulse or a non-layer-selective excitation pulse.

[0014] Furthermore, when the imaging sequence excitation pulse is a layer-selective excitation pulse, after the refocusing pulse frequency parameter is determined, the layer-selective gradient is no longer applied while the refocusing pulse is applied, thereby achieving selective refocusing of water signals.

[0015] Furthermore, the magnetic resonance imaging is high-field or ultra-high-field magnetic resonance imaging.

[0016] A method for determining the refocusing pulse frequency parameter in high-field magnetic resonance imaging (MRI) is provided. The first precession frequency of the target imaging material under the main magnetic field strength is used as the center frequency of the refocusing pulse. The difference between the two precession frequencies of the target imaging material and the interfering imaging material under the main magnetic field determines the bandwidth of the refocusing pulse frequency, ensuring that the refocusing magnetic resonance signal does not contain the magnetic resonance signal of the interfering imaging material.

[0017] The beneficial effects of this invention are as follows: The high-field magnetic resonance imaging method of this invention uses the first precession frequency of the target imaging material under the main magnetic field strength as the center frequency of the convergence pulse, thereby suppressing the target imaging interference signal. It achieves reasonable suppression of the magnetic resonance signal of the interfering imaging material without the need for additional pulses, and overcomes the problems of traditional signal suppression being sensitive to the radio frequency field and poor imaging effect caused by the non-uniformity of the radio frequency field. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the high-field magnetic resonance imaging method of the present invention;

[0019] Figure 2a This is a schematic diagram of a traditional fast auto-echo sequence.

[0020] Figure 2b This is a schematic diagram of the rapid self-selected echo for fat signal processing according to the present invention;

[0021] Figure 3 This is a schematic diagram of the magnetic resonance imaging device of the present invention. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0023] This invention discloses a high-field magnetic resonance imaging method that uses an imaging sequence with excitation pulses and retraction pulses for magnetic resonance imaging. First, a radio frequency pulse is applied to the human tissue being examined, which is located in a main magnetic field. This radio frequency pulse excites the target region of the tissue. Then, the precession frequencies of the imaging protons in the interfering imaging material and the target imaging material in the main magnetic field are obtained in advance. Based on these two precession frequencies, the retraction pulse frequency parameters that prevent the interfering imaging material from retracting are determined. Finally, the imaging sequence with adjusted parameters is used for magnetic resonance imaging. If there is a retraction gradient in the imaging sequence, the retraction gradient parameters of the imaging sequence need to be adjusted accordingly based on the determined retraction pulse frequency parameters. It should be noted that the high-field magnetic resonance in this embodiment mainly refers to magnetic resonance scanning systems with a main magnetic field strength of 3 Tesla (T), 5T, 7T, or higher.

[0024] like Figure 1 The diagram shows a schematic flow chart of the magnetic resonance imaging method of the present invention. This embodiment is applicable to situations involving magnetic resonance scanning imaging, particularly when using an imaging sequence that simultaneously provides excitation and convergence pulses. This method can be executed by a magnetic resonance imaging device, which can be implemented in software and / or hardware; for example, the magnetic resonance imaging device can be configured in a computer device. Figure 1 As shown, the method includes:

[0025] S110 generates the main magnetic field.

[0026] In this embodiment, the main magnetic field can be generated by a main magnet. The main magnet can surround and form a cavity or space with a accommodating space. During magnetic resonance signal acquisition, the subject can be placed into the cavity or space, the main magnet generates the main magnetic field, and the subject is located within the field of view formed by the main magnetic field. The main magnet can generally be a coil or a permanent magnet. In this embodiment, the main magnet is a superconducting coil, and computer equipment controls the main magnet to generate the main magnetic field.

[0027] The main magnet generates a highly uniform and stable static magnetic field, causing protons within the examined tissue to form magnetic moments and controlling their spin at the Larmor frequency along the magnetic field direction. Simultaneously, the nuclear magnetic resonance generated by the proton spin interacts with the main magnetic field, causing precession. The magnetic field strength of the main magnetic field can be set according to actual needs. Within a certain range, a higher main magnetic field strength results in a higher signal-to-noise ratio for the image.

[0028] In this embodiment, the main magnetic field can be a 5T high field or an ultra-high field of 5T or more.

[0029] S120, emits radio frequency pulses to stimulate the target area of ​​the subject.

[0030] In this embodiment, the video pulse is emitted by an RF transmitting coil. The RF pulse parameters can be set according to actual needs. For example, the number of RF pulses and the flip angle can be determined according to the target area of ​​the subject and imaging requirements. The RF pulse can be adiabatic or non-adiabatic, and its excitation method can be selective or non-selective. The number of RF pulses can be one or more, and the flip angle can be 90°. Taking fast spin echo as an example, the number of RF pulses is one, and the flip angle is 90°. The target area contains various different substances or the same substance, such as water, fat, muscle, bone, and various organ tissues.

[0031] S130. A refocusing pulse is emitted to refocus the magnetic resonance signal in the target region. The refocusing pulse frequency parameter is determined based on the precession frequency of the imaging protons within different substances. These different substances can be different substances located within the target region. To address the technical problem of uneven suppression of interference signals (such as fat signals) in existing technologies, this embodiment utilizes the frequency selectivity of the refocusing pulse in an imaging sequence that simultaneously possesses excitation and refocusing pulses. By setting appropriate refocusing pulse frequency parameters, the magnetic resonance signal is refocused only at specific frequencies, thereby achieving reasonable suppression of interference signals and improving the signal-to-noise ratio. For example, the imaging sequence simultaneously possessing excitation and refocusing pulses can be spin echo imaging, fast spin echo imaging, spin echo planar imaging, etc. The refocusing pulse can be an adiabatic pulse or a non-adiabatic pulse, and there can be one or more refocusing pulses in the imaging sequence. Multiple signal acquisition modules can be located between adjacent refocusing pulses; the specific settings can be determined according to actual needs and are not limited here. Taking fast spin echo as an example, there are multiple convergence pulses, and adjacent convergence pulses are directly set with a gradient pulse sequence to receive the magnetic resonance signal. The convergence pulses are emitted by the radio frequency transmitting coil.

[0032] During magnetic resonance imaging (MRI), protons in different substances within the subject's body undergo precession. The same magnetic atomic nucleus, in the same magnetic field environment, should have the same precession frequency if not interfered with by other factors. However, substances generally exist in molecular form, and other atomic nuclei or electrons within a molecule will influence a particular magnetic atomic nucleus. That is, the same magnetic atomic nucleus will have different precession frequencies in different molecules, even under the same uniform main magnetic field. In the field of MRI, this phenomenon is called chemical shift. The degree of chemical shift is directly proportional to the strength of the main magnetic field; the higher the field strength, the more pronounced the chemical shift. In conventional MRI, the object being imaged is the proton, and the precession frequency of protons in different molecules will also differ. In human tissue, the most typical proton chemical shift phenomenon exists between water and fat. The precession frequency difference between water molecules and fat molecules is approximately 3.4 ppm, which translates to a difference of 440 Hz at a 3T field strength and approximately 220 Hz at a 1.5T field strength. The different precession frequencies of protons in water and fat can lead to misalignment of materials during imaging. Based on this, the refocusing pulse frequency parameters can be determined according to the precession frequencies of imaging protons in different materials, so that during the refocusing of the magnetic resonance signal, only the magnetic resonance signal of the target imaging material is refocused.

[0033] The target imaging material and interfering imaging material can be determined according to actual needs. Optionally, the target imaging material and interfering imaging material can be at least one of water, fat, muscle, bone, or various organ tissues, and the target imaging material and interfering imaging material can be different substances. That is, the target imaging material and interfering imaging material can both be at least one of water, fat, muscle, bone, or various organ tissues, but the imaging protons in the target imaging material and the interfering imaging material need to have different precession frequencies. It can be understood that the imaging protons can be determined according to imaging requirements. For example, the imaging protons are generally protons in hydrogen (H) atoms, but can also be protons in phosphorus (P) atoms, sodium (Na) atoms, nitrogen (N) atoms, carbon (C) atoms, fluorine (F) atoms, etc. For example, when it is necessary to acquire water signals and suppress fat signals, the target imaging material is water, and the interfering imaging material is fat. When it is necessary to acquire fat signals and suppress water signals, the target imaging material is fat, and the interfering imaging material is water.

[0034] In another example, the target imaging material and the interfering imaging material can be the same type of substance, such as different types of fat, different tissues / organs, different muscles, or different bones. Taking fat as an example, fat molecules have a large molecular formula, and the precession frequencies of H atoms at different positions in the chemical formula are different. When it is necessary to suppress low-frequency H atom signals and acquire high-frequency H atom signals, both the target imaging material and the interfering imaging material are fat. Furthermore, because the precession frequencies of H atoms in fat molecules vary considerably, some H atoms have precession frequencies close to those in water. When it is necessary to suppress water signals and acquire fat signals, H atoms in fat with precession frequencies close to those in water will be suppressed simultaneously. In this case, the target imaging material is fat, and the interfering imaging materials are water and fat. In summary, the target imaging material and the interfering imaging material are determined by the suppressed precession frequency and the acquired precession frequency. The target imaging material and the interfering imaging material can be the same substance or different substances.

[0035] In this embodiment, the refocusing pulse frequency parameter includes the refocusing pulse center frequency. The method for determining the refocusing pulse parameter includes: acquiring the first precession frequency of the target imaging material under the main magnetic field strength, and using the first precession frequency as the refocusing pulse center frequency. Taking water as the target imaging material as an example, the precession frequency of water under the main magnetic field strength is used as the first precession frequency, and the first precession frequency is used as the refocusing pulse center frequency. In specific settings, a calibration frequency can be acquired. When the calibration frequency is the first precession frequency, no adjustment is needed. When the calibration frequency is not the first center frequency, the refocusing pulse center frequency is adjusted to the first precession frequency. Setting the refocusing pulse center frequency ensures that the refocused magnetic resonance signal is the magnetic resonance signal of the target imaging material. Further, the precession frequency of the target imaging material under the main magnetic field strength can be obtained according to a pre-set mapping table or calculation formula. Even further, the precession frequency of the target imaging material under the main magnetic field strength can be obtained according to magnetic resonance scanning data, that is, the frequency parameter can be adjusted according to historical data or adjusted in real time.

[0036] Based on the above scheme, the refocusing pulse frequency parameter also includes the refocusing pulse frequency bandwidth. The method for determining the refocusing pulse bandwidth includes: obtaining the first precession frequency of the imaging proton in the target imaging material and the second precession frequency of the imaging proton in the interfering imaging material under the main magnetic field strength; determining the precession frequency difference between the first and second precession frequencies; and determining the refocusing pulse frequency bandwidth based on the precession frequency difference. The refocusing pulse bandwidth can be understood as the pulse width of the refocused magnetic resonance signal. A reasonable setting of the refocusing pulse bandwidth can ensure that the refocused magnetic resonance signal does not contain the magnetic resonance signal of the interfering imaging material. For example, taking a main magnetic field strength of 3T, a target imaging material of water, and an interfering imaging material of fat as an example, the difference in precession frequencies between water and fat under the main magnetic field strength is 440Hz. Therefore, the precession frequency of water is used as the center frequency of the refocusing pulse, and the refocusing pulse bandwidth is determined based on 440Hz to ensure that only the water signal is refocused, and the fat signal is not refocused. Furthermore, based on a pre-set mapping table or calculation formula, the precession frequency and / or the difference in precession frequency between the target imaging material and the interfering imaging material under the main magnetic field strength can be obtained.

[0037] Optionally, the recoiling pulse frequency bandwidth can be determined based on the precession frequency difference, including: using any precession frequency less than twice the precession frequency difference as the recoiling pulse frequency bandwidth. Considering that the recoiling pulse is symmetrically covered (i.e., if the recoiling pulse bandwidth is BW), then the left and right sides of the recoiling pulse center frequency respectively cover a frequency range of BW / 2. Therefore, using any precession frequency less than twice the precession frequency difference as the recoiling pulse frequency bandwidth ensures that the recoiling signal does not contain magnetic resonance signals from interfering substances. For example, if the precession frequency difference between water and fat under a 3T main magnetic field is 440Hz, then the recoiling pulse frequency bandwidth should be set to be less than 880Hz, for example, 300Hz.

[0038] Optionally, a percentage can be preset according to imaging requirements, using the percentage of the precession frequency difference as the convergence pulse bandwidth. For example, the percentage can be preset to 60%, meaning 60% of the precession frequency difference is used as the convergence pulse bandwidth. If the precession frequency difference between water and fat under a 3T main magnetic field is 440Hz, then the convergence pulse frequency bandwidth can be set to 264Hz.

[0039] S140: Receive magnetic resonance signals and reconstruct magnetic resonance signals to generate magnetic resonance images of the target region.

[0040] In this embodiment, by reasonably setting the retraction pulse frequency parameters, only the magnetic resonance signal of the target imaging material is retracted. Based on this, the radio frequency receiving coil can only receive the retracted magnetic resonance signal of the target imaging material, and the magnetic resonance image can be directly reconstructed based on the acquired magnetic resonance signal containing only the target imaging material. The magnetic resonance signal can be received by the radio frequency receiving coil. The radio frequency transmitting coil and the radio frequency receiving coil can be the same radio frequency coil or different radio frequency coils.

[0041] Figure 2a This is a schematic diagram of a traditional fast auto-echo sequence. Figure 2b This is a schematic diagram of the fast spin echo method for fat signal suppression according to the present invention. The magnetic resonance imaging method provided in this embodiment will be explained using fast spin echo suppression of fat signals as an example. Figure 2b The imaging sequence excitation pulse can be either a slice-selective excitation pulse or a non-slice-selective excitation pulse. In this embodiment, a 90° radio frequency (RF) excitation pulse is selected, and a slice-selective gradient is applied simultaneously with the RF excitation pulse along the slice selection gradient (Gss) direction to form the slice-selective excitation pulse. The bandwidth of the refocusing pulse is pre-determined based on the difference in precession frequencies of water and fat under the main magnetic field. In the figure, a dephasing gradient along the slice selection gradient (Gss) direction is also symmetrically applied on both sides of the frequency-selective refocusing pulse.

[0042] For example, if the frequency of the main magnetic field is f0, then the frequency difference between water and fat is 3.4 × 10⁻⁶. -6 ×f0, setting the reverberation pulse bandwidth to half the frequency difference between water and fat, i.e., 1.7 × 10⁻⁶. -6 ×f0. If the imaging target is water signals, and fat signals need to be suppressed, then the frequency of the refocusing pulse is set to the main magnetic field frequency f0. After applying the radio frequency excitation pulse RF, a refocusing pulse is applied based on the determined refocusing pulse bandwidth and center frequency. Furthermore, while applying the refocusing pulse, no layer selection gradient is applied. This achieves selective refocusing of water signals while preventing the refocusing of fat signals with frequencies significantly different from water signals, thus suppressing fat signals and solving the problem of fat suppression being sensitive to the radio frequency field (B1) under high field conditions.

[0043] In one embodiment, if the imaging target is the fat signal while suppressing the water signal, the frequency of the refocusing pulse can be set to f0 = 3.4 × 10⁻⁶. -6 ×f0 is used to ensure that the refocusing pulse refocuses the fat signal but not the water signal. After applying the radio frequency excitation pulse RF, a refocusing pulse is applied based on the determined refocusing pulse bandwidth and center frequency. Furthermore, the layer selection gradient is not applied simultaneously with the refocusing pulse, achieving selective refocusing of the fat signal while preventing the refocusing of the water signal, which has a significantly different frequency from the fat signal, thus suppressing the water signal. Further, after the 90° radio frequency excitation pulse, multiple refocusing pulses (frequency-selective refocusing pulses) are applied consecutively. Each refocusing pulse can be set to the same center frequency and bandwidth, and the flip angle of each refocusing pulse can be set differently according to the actual scanning requirements. The magnetic resonance signals generated by the same excitation can fill the same K-space to achieve rapid acquisition of magnetic resonance signals under high field conditions.

[0044] In existing technologies, fat signal suppression is sometimes necessary in clinical settings, reducing imaging efficiency and causing inconvenience for drug-sensitive patients. This embodiment achieves fat signal suppression without requiring additional fat suppression pulses, reducing adverse patient reactions and overcoming the limitation of traditional fat suppression being sensitive to the B1 field. Furthermore, compared to the conventional approach of applying a fat suppression pulse sequence before the imaging sequence, this application eliminates the need for a fat suppression pulse sequence, effectively reducing the absorption of radio frequency energy by the target object in a high-field magnetic resonance system, resulting in a reduced specific absorption rate (SAR).

[0045] This invention generates a main magnetic field; emits radio frequency pulses to excite the target area of ​​the subject; emits convergence pulses to converge the magnetic resonance signal of the target area, wherein the convergence pulse frequency parameter is determined according to the precession frequency of the imaging protons in different substances; receives the magnetic resonance signal, reconstructs the magnetic resonance signal to generate a magnetic resonance image of the target area. By reasonably setting the convergence pulse parameters, only the magnetic resonance signal of the target imaging substance is converged, thus achieving reasonable suppression of the magnetic resonance signal of the interfering imaging substance without additional pulses. This overcomes the problems of traditional signal suppression being sensitive to the radio frequency field and poor imaging effect caused by the non-uniformity of the radio frequency field.

[0046] Figure 3 This is a schematic diagram of a magnetic resonance imaging (MRI) device. This invention can be implemented in software and / or hardware; for example, the MRI device can be integrated into a computer device. Figure 3 As shown, the device includes a main magnetic field control module 210, a radio frequency pulse control module 220, a refocusing pulse control module 230, and a signal processing module 230, wherein:

[0047] The main magnetic field control module 210 is used to control the main magnet to generate the main magnetic field.

[0048] The radio frequency pulse control module 220 is used to control the radio frequency transmitting coil to emit radio frequency pulses to excite the target area of ​​the subject.

[0049] The refocusing pulse control module 230 is used to control the radio frequency transmitting coil to emit refocusing pulses to refocus the magnetic resonance signal in the target area. The refocusing pulse frequency parameter is determined according to the precession frequency of the imaging protons in different substances.

[0050] The signal processing module 240 is used to control the radio frequency receiving coil to receive magnetic resonance signals and generate magnetic resonance image data.

[0051] In this embodiment of the invention, a main magnetic field control module controls a main magnet to generate a main magnetic field; a radio frequency pulse control module controls a radio frequency transmitting coil to emit radio frequency pulses to excite the target area of ​​the subject; a refocusing pulse control module controls a radio frequency transmitting coil to emit refocusing pulses to refocus the magnetic resonance signal of the target area. The refocusing pulse frequency parameter is determined based on the precession frequency of the imaging protons in different substances; and a signal processing module controls a radio frequency receiving coil to receive the magnetic resonance signal and generate magnetic resonance image data. By reasonably setting the refocusing pulse parameters, only the magnetic resonance signal of the target imaging substance is refocused, thus achieving reasonable suppression of the magnetic resonance signal of the interfering imaging substance without the need for additional pulses. This overcomes the problems of traditional signal suppression being sensitive to the radio frequency field and poor imaging effects caused by inhomogeneous radio frequency fields.

[0052] Optionally, the magnetic resonance imaging system can be a high-field or ultra-high-field magnetic resonance imaging system.

[0053] Optionally, based on the above scheme, the device further includes a re-polymer pulse parameter determination module. The re-polymer pulse frequency parameter includes the center frequency of the re-polymer pulse. The re-polymer pulse parameter determination module is used for:

[0054] The first precession frequency of the target imaging material under the main magnetic field strength is obtained, and the first precession frequency is used as the center frequency of the refocusing pulse.

[0055] Optionally, based on the above scheme, the recoil pulse frequency parameter also includes the recoil pulse frequency bandwidth, and the recoil pulse parameter determination module is further used for:

[0056] The first precession frequency of the imaging proton in the target imaging material and the second precession frequency of the imaging proton in the interfering imaging material are obtained under the main magnetic field strength.

[0057] The difference between the precession frequencies of the first and second precession frequencies is determined, and the bandwidth of the retraction pulse frequency is determined based on the difference in precession frequencies.

[0058] Optionally, based on the above scheme, the re-convergence pulse parameter determination module is specifically used for:

[0059] Any precession frequency less than twice the precession frequency difference is used as the retraction pulse frequency bandwidth.

[0060] Optionally, based on the above scheme, the target imaging material and the interfering imaging material are respectively at least one of water, fat, muscle, bone, and various organ tissues, and the imaging protons in the target imaging material and the interfering imaging material have different precession frequencies.

[0061] The magnetic resonance imaging device provided in the embodiments of the present invention can execute the magnetic resonance imaging method provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of executing the method.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-field magnetic resonance imaging method, using an imaging sequence with excitation pulses and convergence pulses for magnetic resonance imaging, characterized in that, First, a radio frequency pulse is applied to the human tissue being examined, which is in the main magnetic field. The number of radio frequency pulses and the flip angle in the radio frequency pulse parameters are determined according to the target area of ​​the human tissue being examined. Then, the precession frequencies of the target imaging material and the interfering imaging material under the main magnetic field are obtained in advance. Based on the two obtained precession frequencies, the re-convergence pulse frequency parameters of the non-convergence interfering imaging material are determined. The re-convergence pulse frequency parameters include the re-convergence pulse center frequency and the re-convergence pulse frequency bandwidth. The first precession frequency of the target imaging material under the main magnetic field strength is used as the re-convergence pulse center frequency. The difference between the two precession frequencies of the target imaging material and the interfering imaging material under the main magnetic field determines the re-convergence pulse frequency bandwidth, ensuring that the reconciled magnetic resonance signal does not contain the magnetic resonance signal of the interfering imaging material. Finally, magnetic resonance imaging was performed using an imaging sequence with defined parameters.

2. The high-field magnetic resonance imaging method according to claim 1, characterized in that, The recoil pulse frequency bandwidth is determined by any precession frequency less than twice the difference between the two precession frequencies.

3. The high-field magnetic resonance imaging method according to claim 1, characterized in that, The target imaging substance and the interfering imaging substance are determined according to actual needs. The target imaging substance and the interfering imaging substance are at least one of water, fat, muscle, bone, and various organ tissues. The target imaging substance and the interfering imaging substance are different substances.

4. The high-field magnetic resonance imaging method according to claim 1, characterized in that, The target imaging material and the interfering imaging material are determined according to actual needs. The target imaging material and the interfering imaging material are atoms with different precession frequencies in the same type of material.

5. The high-field magnetic resonance imaging method according to any one of claims 1 to 4, characterized in that, The excitation pulse in the imaging sequence can be a layer-selective excitation pulse or a non-layer-selective excitation pulse.

6. The high-field magnetic resonance imaging method according to claim 5, characterized in that, When the excitation pulse in the imaging sequence is a layer-selective excitation pulse, after the refocusing pulse frequency parameter is determined, the layer-selective gradient is no longer applied while the refocusing pulse is applied, thereby achieving selective refocusing of water signals.

7. The high-field magnetic resonance imaging method according to claim 5, characterized in that, The magnetic resonance imaging is high-field or ultra-high-field magnetic resonance imaging.

8. A method for determining the refocusing pulse frequency parameter in high-field magnetic resonance imaging, characterized in that, The first precession frequency of the target imaging material under the main magnetic field strength is used as the center frequency of the reconvergence pulse. The difference between the two precession frequencies of the target imaging material and the interfering imaging material under the main magnetic field determines the bandwidth of the reconvergence pulse frequency, ensuring that the magnetic resonance signal of the reconverged magnetic resonance signal does not contain the magnetic resonance signal of the interfering imaging material.

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