A b1 field correction method and device for precise quantification of CEST signal

Abstract

This invention relates to the field of biomedical engineering, specifically to a B1 field correction method and apparatus for accurate quantification of CEST signals. The method and apparatus include: acquiring CEST data from two B1 energy labels and calculating their respective CEST' signals; obtaining the actual energy B1 field relative spatial distribution. 1rms Establishing the CEST signal and actual energy B 1rms The linear functional relationship between ' and ' is used to fit the coefficients of the linear function; from the fitted linear function, the actual energy B after field correction for B1 is calculated. 1rms The corresponding CEST signal. This invention establishes a linear functional relationship between the CEST signal and B1, enabling simple and effective correction of B1, which helps to accurately quantify the CEST signal.

Description

Technical Field

[0001] This invention relates to the field of biomedical engineering, and more specifically, to a B1 field correction method and apparatus for accurate quantification of CEST signals. Background Technology

[0002] Chemical exchange saturation transfer (CEST) imaging is an important imaging method for non-invasively acquiring molecular-level information of biological tissues using endogenous or exogenous CEST contrast agents. CEST imaging is a magnetic resonance molecular imaging technique capable of probing the microscopic environment of biological tissues. It can measure endogenous metabolites, compounds (such as glucose, glycogen, and amide protons), and exogenous paramagnetic / diamagnetic CEST contrast agents, providing new methods for imaging various diseases (such as stroke, tumors, and epilepsy). The CEST signal is closely related to parameters such as the applied radiofrequency field (B1) energy, and the strength of the CEST signal is closely related to the radiofrequency energy used to label the CEST contrast agent. However, due to hardware system deviations, the B1 field often exhibits spatial distribution differences, especially in large-aperture, high-field-strength human magnetic resonance imaging systems. This problem is more pronounced, leading to differences in CEST signals from the same tissue, inaccurate quantification, and difficulties in disease detection and assessment.

[0003] Existing methods for correcting the B1 field are relatively limited, mainly including:

[0004] (1) Correction method based on analytical solution of dual-pool Bloch-McConnell equation [Sun et al., MagneticResonance in Medicine 2007; 58:1207-1215]. This method first obtains the spatial distribution of the B1 field through dual-flip angle gradient echo imaging, and acquires and measures the main magnetic field offset field map B0, as well as the longitudinal relaxation T1 and transverse relaxation T2 of the tissue. B1 field correction is then implemented by combining the analytical expression of the Bloch-McConnell equation for the CEST signal. This method not only requires a large amount of additional information and involves cumbersome data processing, but it is also only applicable to CEST imaging scenarios using continuous radio frequency pulse markers. For pulsed radio frequency pulse markers, since their CEST signals do not have an analytical expression, the above-mentioned B1 field correction method is difficult to apply.

[0005] (2) Polynomial fitting method based on subjective experience [Singh et al., Magnetic Resonance in Medicine 2013; 69:818-824]: First, the relative spatial distribution map of the B1 field (B1) is obtained using the double flip angle gradient echo imaging method. 1rel Then, multiple B1 energies (B) are collected. 1rmsThe actual energy B is obtained from the CEST magnetic resonance data. 1rms '=B 1rms xB 1rel Choose B 1rel The closest to 1 (i.e., B) 1rms '≈B 1rms The region is defined, and the corresponding CEST signal is calculated. cal ), establish CEST cal Signal follows B 1rms The changing second-order polynomial, namely CEST cal =p2xB 1rms 2 +p1xB 1rms +p0, thus the coefficients p2, p1, and p0 of the polynomial are obtained by fitting. Therefore, the CEST signal after B1 correction is CEST = CEST' + (p2xB0) / p1 + (p2xB0) / p2 + (p1 ... 1rms 2 +p1xB 1rms )-(p2xB 1rms ' 2 +p1xB 1rms The method uses CEST as the CEST signal before B1 correction. However, this method requires acquiring more than three sets of magnetic resonance CEST data corresponding to B1 energies, resulting in a long imaging time. Furthermore, if the B1 energy to be corrected exceeds B1, the method may fail to achieve the desired effect. 1rms The range of extrapolation will reduce the accuracy of the correction due to errors; furthermore, if B is not present in a certain tissue... 1rel In regions close to 1, the tissue cannot be B1 corrected using the above method. Therefore, the limitations of this B1 correction method are quite evident. Summary of the Invention

[0006] This invention provides a B1 field correction method and apparatus for accurate quantitative analysis of CEST signals, thereby at least solving the technical problem of the difficulty in applying existing B1 field correction methods.

[0007] According to an embodiment of the present invention, a B1 field correction method for accurate quantification of CEST signals is provided, comprising the following steps:

[0008] Collect CEST data from two B1 energy markers and calculate their respective CEST' signals;

[0009] Obtain the actual energy B of the relative spatial distribution of the B1 field. 1rms ';

[0010] Establishing the CEST signal and actual energy B 1rms The linear functional relationship between ' and ', and the coefficients of the fitted linear function;

[0011] Calculate the actual energy B after field correction from the fitted linear function. 1rms The corresponding CEST signal.

[0012] Furthermore, CEST data for two B1 energy markers were acquired, and their respective CEST' signals were calculated, including:

[0013] Two B1-energy labeled magnetic resonance signals were acquired, normalized, and the CEST' signal was calculated, where CEST' = 1 / Z. label -1 / Z ref Among them, Z label Z represents the magnetic resonance signal generated by water and CEST contrast agent at the target CEST contrast agent resonance frequency Δω. ref Conventional data preprocessing is used to correct the main magnetic field offset of the magnetic resonance signal generated by water molecules relative to the resonance frequency -Δω on the opposite side of the water molecule.

[0014] Furthermore, when normalizing the signal, Z = S / S0, where S is the magnetic resonance signal with radio frequency pulse marking and S0 is the magnetic resonance signal without radio frequency pulse marking.

[0015] Furthermore, obtain the actual energy B of the relative spatial distribution of the B1 field. 1rms 'include:

[0016] The actual energy B1 relative spatial distribution of the B1 field was obtained using the double-flip angle gradient echo imaging method. 1rms '.

[0017] Furthermore, the actual energy B of the relative spatial distribution of the B1 field was obtained using the double-flip angle gradient echo imaging method. 1rms 'include:

[0018] The relative spatial distribution of field B1 was obtained using the double-flip-angle gradient echo imaging method. 1rel Let the flip angles be θ and 2θ, and the corresponding images be I1 and I2, then B 1rel B is obtained using the arccosine algorithm Arccos. 1rel =arccos(I2 / 2I1) / θ, actual labeled energy B 1rms '=B 1rms xB 1rel .

[0019] Furthermore, a linear functional relationship is established between the CEST' signal and the actual energy B1rms'. The coefficients of the fitted linear function include:

[0020] Establish CEST and B 1rms Linear function relationship, 1 / CEST=k / ω1 2 +b, where ω 1＝γ·B 1rms gyromagnetic ratio γ = 42.6 MHz / T;

[0021] Energy B is actually labeled 1rms The k and b parameters in the linear function model are fitted to the corresponding signal CEST.

[0022] Furthermore, the actual energy B after field correction is calculated from the fitted linear function. 1rms The corresponding CEST signals include:

[0023] Based on the established linear function 1 / CEST=k / ω1 2 +b, CEST=1 / (k / ω1) 2 +b), to obtain B 1rms The corresponding CEST signal.

[0024] According to another embodiment of the present invention, a B1 field correction device for accurate quantification of CEST signals is provided, comprising:

[0025] The data acquisition unit is used to acquire CEST data from two B1 energy markers and calculate their respective CEST' signals.

[0026] The energy acquisition unit is used to acquire the actual energy B of the B1 field relative spatial distribution. 1rms ';

[0027] Function fitting unit, used to establish the relationship between the CEST' signal and the actual energy B 1rms The linear functional relationship between ' and ', and the coefficients of the fitted linear function;

[0028] The signal calculation unit is used to calculate the actual energy B after field correction from the fitted linear function. 1rms The corresponding CEST signal.

[0029] A storage medium storing a program file capable of implementing any of the above-mentioned B1 field correction methods for accurate quantification of CEST signals.

[0030] A processor for running a program, wherein the program executes any of the above-mentioned B1 field correction methods for accurate quantification of CEST signals.

[0031] The B1 field correction method and apparatus for accurate quantification of CEST signals in this embodiment of the invention can achieve simple and effective B1 correction by establishing a linear functional relationship between the CEST signal and B1, which helps to accurately quantify the CEST signal. Attached Figure Description

[0032] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0033] Figure 1 This is a flowchart of the B1 field correction method for accurate quantitative analysis of CEST signals according to the present invention.

[0034] Figure 2 This is a diagram showing the relative spatial distribution of the B1 field in this invention;

[0035] Figure 3 The spatial distribution of creatine biomimetic CEST signals at radio frequency pulse energies of 0.75 μT and 1.25 μT in this invention is shown.

[0036] Figure 4 This is the B1 field correction diagram based on the linear function model in this invention;

[0037] Figure 5 This is a spatial distribution diagram of the creatine biomimetic CEST signal corresponding to RF marker energies of 0.75 μT and 1.25 μT after B1 RF field correction in this invention.

[0038] Figure 6 This is a block diagram of the B1 field correction device for accurate quantitative analysis of CEST signals according to the present invention. Detailed Implementation

[0039] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0040] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0041] Example 1

[0042] According to an embodiment of the present invention, a B1 field correction method for accurate quantification of CEST signals is provided, see [link to relevant documentation]. Figure 1 This includes the following steps:

[0043] S101: Collect CEST data from two B1 energy markers and calculate their respective CEST' signals;

[0044] S102: Obtain the actual energy B of the relative spatial distribution of the B1 field. 1rms ';

[0045] S103: Establishing the CEST signal and actual energy B 1rms The linear functional relationship between ' and ', and the coefficients of the fitted linear function;

[0046] S104: Calculate the actual energy B after field correction from the fitted linear function. 1rms The corresponding CEST signal.

[0047] The B1 field correction method for accurate quantification of CEST signals in this embodiment of the invention establishes a linear functional relationship between the CEST signal and B1, which enables simple and effective B1 correction and helps to accurately quantify the CEST signal.

[0048] The process of acquiring CEST data from two B1 energy markers and calculating their respective CEST' signals includes:

[0049] Two B1-energy labeled magnetic resonance signals were acquired, normalized, and the CEST' signal was calculated, where CEST' = 1 / Z. label -1 / Z ref Among them, Z label Z represents the magnetic resonance signal generated by water and CEST contrast agent at the target CEST contrast agent resonance frequency Δω. ref Conventional data preprocessing is used to correct the main magnetic field offset of the magnetic resonance signal generated by water molecules relative to the resonance frequency -Δω on the opposite side of the water molecule.

[0050] When normalizing the signal, Z = S / S0, where S is the magnetic resonance signal with radio frequency pulse marking and S0 is the magnetic resonance signal without radio frequency pulse marking.

[0051] Among them, the actual energy B of the relative spatial distribution of field B1 is obtained. 1rms 'include:

[0052] The actual energy B1 relative spatial distribution of the B1 field was obtained using the double-flip angle gradient echo imaging method. 1rms '.

[0053] Among them, the actual energy B of the relative spatial distribution of the B1 field is obtained by using the double-flip angle gradient echo imaging method. 1rms 'include:

[0054] The relative spatial distribution of field B1 was obtained using the double-flip-angle gradient echo imaging method. 1rel Let the flip angles be θ and 2θ, and the corresponding images be I1 and I2, then B 1rel B is obtained using the arccosine algorithm Arccos. 1rel =arccos(I2 / 2I1) / θ, actual labeled energy B 1rms '=B 1rms xB 1rel .

[0055] Among them, the CEST' signal and the actual energy B are established. 1rms The linear functional relationship between ' and ', and the coefficients of the fitted linear function include:

[0056] Establish CEST and B 1rms Linear function relationship, 1 / CEST=k / ω1 2 +b, where ω 1＝ γ·B 1rms gyromagnetic ratio γ = 42.6 MHz / T;

[0057] Energy B is actually labeled 1rms The k and b parameters in the linear function model are fitted to the corresponding signal CEST.

[0058] Among them, the actual energy B after field correction is calculated from the fitted linear function. 1rms The corresponding CEST signals include:

[0059] Based on the established linear function 1 / CEST=k / ω1 2 +b, CEST=1 / (k / ω1) 2 +b), to obtain B 1rms The corresponding CEST signal.

[0060] The B1 field correction method for accurate quantification of CEST signals according to the present invention will be described in detail below with specific embodiments:

[0061] To address the shortcomings of existing technologies, this invention proposes a novel B1 field correction scheme. By establishing a linear functional relationship between the CEST signal and B1, B1 correction can be achieved simply and effectively, which helps to accurately quantify the CEST signal.

[0062] This invention proposes a B1 field correction method for accurate quantification of CEST signals, which mainly consists of the following: (1) acquiring two B1 energies (B 1rmsThe CEST data is marked and the respective CEST signals are calculated, i.e., CEST' = 1 / Z. label -1 / Z ref Among them, Z label Z represents the magnetic resonance signal at the target CEST contrast agent resonance frequency. ref (2) Obtain the relative spatial distribution map of the B1 field (B1) based on the double-flip angle gradient echo imaging method at the magnetic resonance frequency opposite to that of water molecules; 1rel If the actual energy B is... 1rms '=B 1rms xB 1rel (3) Establish CEST' signal and B 1rms (3) Determine the linear function relationship and fit the coefficients of the linear function; (4) Calculate the B1 field-corrected B from the fitted linear function. 1rms The corresponding CEST signal. Specifically:

[0063] 1. Collect two B1 energies (B 1rms The magnetic resonance signals marked with radio frequency pulses (RF pulses) undergo routine data preprocessing, including signal normalization (i.e., Z = S / S0, where S is the RF pulse-marked MRI signal and S0 is the non-RF pulse-marked MRI signal) and main magnetic field offset correction. The CEST signal is then calculated, i.e., CEST' = 1 / Z. label -1 / Z ref Among them, Z label Z represents the magnetic resonance signal generated by water and CEST contrast agent at the target CEST contrast agent resonance frequency (Δω). ref The magnetic resonance signal generated by water molecules is at the resonance frequency (-Δω) opposite to that of water molecules.

[0064] 2. Obtain the relative spatial distribution map of the B1 field (B1 field) using the double-flip angle gradient echo imaging method. 1rel Let the flip angles be θ and 2θ, and the corresponding images be I1 and I2. Then B 1rel It can be obtained using the arccosine algorithm, i.e., B. 1rel =arccos(I2 / 2I1) / θ. Therefore, the actual labeled energy B 1rms '=B 1rms xB 1rel .

[0065] 3. Establish CEST and B 1rms The linear functional relationship is 1 / CEST = k / ω1 2 +b, where ω 1＝ γ·B 1rms The gyromagnetic ratio γ = 42.6 MHz / T. This is derived from the actual labeled energy B. 1rmsThe parameters such as k and b in the linear function model are fitted to the corresponding signal CEST.

[0066] 4. Based on the established linear function 1 / CEST=k / ω1 2 +b, then CEST=1 / (k / ω1) 2 +b) will give you B 1rms The corresponding ideal CEST signal is obtained, thereby solving the influence of B1 field inhomogeneity and achieving accurate quantification of CEST signal.

[0067] The key points and protected points of this invention are at least as follows:

[0068] 1. This invention proposes a B1 correction scheme for radio frequency fields.

[0069] 2. The linear function model correction method for radio frequency field B1 proposed in this invention has the advantages of being simple, fast, and stable, and effectively solves the limitations of existing technologies such as being cumbersome, time-consuming, having limited applicability, and being inaccurate.

[0070] 3. The radio frequency field B1 correction method proposed in this invention is beneficial for the accurate quantification of CEST signals.

[0071] Compared with the prior art, the advantages of the present invention are at least as follows:

[0072] The advantages of this invention include: (1) Compared with the analytical solution correction method based on the dual-pool Bloch-McConnell equation, the technical solution of this invention avoids the limitations of existing methods, such as being cumbersome and time-consuming, only applicable to continuous radio frequency pulse marking methods, and requiring additional information. By establishing a linear relationship between the B1 radio frequency field energy and the CEST signal, the B1 field non-uniformity correction can be achieved, which is simple and fast; (2) Compared with the polynomial fitting method based on subjective experience, the technical solution of this invention does not require the use of B1 field non-uniformity correction method. 1rel By fitting a function model to the region close to 1, it can be applied to a wider range of tissue imaging scenarios, and only two sets of B1 energy CEST data are needed to achieve B1 field inhomogeneity correction, thereby enabling accurate quantification of CEST signals.

[0073] The feasibility of this invention has been confirmed through phantom experiments. The results are as follows:

[0074] Two identical creatine biomimetic solutions with a pH of 6.8 and a concentration of 80 mM were prepared using PBS buffer. B1 radiofrequency field distribution imaging and CEST imaging were performed under a 5 T magnetic resonance field. Imaging parameters such as field of view, spatial resolution, and shimming range were kept consistent for both methods. B1 radiofrequency field distribution imaging used two flip angles of 45° and 90°, with a repetition time TR = 10 s. The calculated relative spatial distribution of the B1 field is as follows: Figure 2As shown, the radio frequency field B1 of phantom 1 (vial 1) is significantly lower than that of phantom 2 (vial 2).

[0075] The radiofrequency pulse labeling energies for CEST imaging were 0.75 μT and 1.25 μT, with a saturation time of 3 s, a recovery time of 3 s, a frequency offset range of -3.5 to 3.5 ppm, and a step size of 0.1 ppm. The creatine CEST signal distributions corresponding to 0.75 μT and 1.25 μT are shown below. Figure 3 The figure shows the spatial distribution of CEST signals of creatine phantoms at radio frequency pulse energies of 0.75 μT and 1.25 μT. When the radio frequency pulse energy is 0.75 μT, the creatine CEST signals of the two phantoms are 0.12 and 0.16, respectively; when the radio frequency pulse energy is 1.25 μT, the creatine CEST signals of the two phantoms are 0.20 and 0.25, respectively. It is evident that under the same radio frequency pulse energy, the signals of identical creatine phantoms exhibit significant differences, confirming that B1 field inhomogeneity affects the accuracy of CEST signal quantization.

[0076] Based on the constructed 1 / CEST=k / ω1 2 The +b function, derived from the actual labeled energy B. 1rms The parameters such as k and b in the linear function model are fitted to the corresponding signal CEST, and then the radio frequency field B1 is obtained after correction. 1rms The corresponding ideal CEST signal, thus resolving the influence of B1 field inhomogeneity, see [link / reference]. Figure 4 This is the B1 field correction plot based on a linear function model.

[0077] The distribution of creatine CEST signal after B1 radio frequency field correction is as follows: Figure 5 The figure shows the spatial distribution of creatine phantom CEST signals at radio frequency labeling energies of 0.75 μT and 1.25 μT after B1 radio frequency field correction. When the radio frequency pulse energy is 0.75 μT, the creatine CEST signals of the two phantoms are 0.14 and 0.16, respectively; when the radio frequency pulse energy is 1.25 μT, the creatine CEST signals of the two phantoms are 0.22 and 0.25, respectively. Compared with before B1 radio frequency field correction, at a radio frequency pulse labeling energy of 0.75 μT, the inhomogeneity of phantom 1 relative to phantom 2 decreased from 25% to 12.5%; at a radio frequency pulse labeling energy of 1.25 μT, the inhomogeneity of phantom 1 relative to phantom 2 decreased from 20% to 12%. It can be seen that the proposed B1 radio frequency field correction scheme effectively improves the influence of B1 radio frequency field inhomogeneity on CEST quantification.

[0078] Example 2

[0079] According to another embodiment of the present invention, a B1 field correction device for accurate quantification of CEST signals is provided, see [link to relevant documentation]. Figure 6 ,include:

[0080] The data acquisition unit 201 is used to acquire the CEST data of the two B1 energy markers and calculate their respective CEST' signals;

[0081] Energy acquisition unit 202 is used to acquire the actual energy B of the relative spatial distribution of field B1. 1rms ';

[0082] Function fitting unit 203 is used to establish the relationship between the CEST' signal and the actual energy B. 1rms The linear functional relationship between ' and ', and the coefficients of the fitted linear function;

[0083] Signal calculation unit 204 is used to calculate the actual energy B after field correction from the fitted linear function. 1rms The corresponding CEST signal.

[0084] The B1 field correction device for accurate quantification of CEST signals in this embodiment of the invention can achieve simple and effective B1 correction by establishing a linear functional relationship between CEST signals and B1, which helps to accurately quantify CEST signals.

[0085] The B1 field correction device for accurate quantification of CEST signals according to the present invention will be described in detail below with specific embodiments:

[0086] To address the shortcomings of existing technologies, this invention proposes a novel B1 field correction scheme. By establishing a linear functional relationship between the CEST signal and B1, B1 correction can be achieved simply and effectively, which helps to accurately quantify the CEST signal.

[0087] This invention proposes a B1 field correction device for accurate quantification of CEST signals, which mainly consists of the following: (1) acquiring two B1 energies (B 1rms The CEST data is marked and the respective CEST signals are calculated, i.e., CEST' = 1 / Z. label -1 / Z ref Among them, Z label Z represents the magnetic resonance signal at the target CEST contrast agent resonance frequency. ref (2) Obtain the relative spatial distribution map of the B1 field (B1) based on the double-flip angle gradient echo imaging method at the magnetic resonance frequency opposite to that of water molecules; 1rel If the actual energy B is... 1rms '=B 1rms xB 1rel (3) Establish CEST' signal and B 1rms (3) Determine the linear function relationship and fit the coefficients of the linear function; (4) Calculate the B1 field-corrected B from the fitted linear function. 1rms The corresponding CEST signal. Specifically:

[0088] 1. Collect two B1 energies (B 1rms The magnetic resonance signals marked with radio frequency pulses (RF pulses) undergo routine data preprocessing, including signal normalization (i.e., Z = S / S0, where S is the RF pulse-marked MRI signal and S0 is the non-RF pulse-marked MRI signal) and main magnetic field offset correction. The CEST signal is then calculated, i.e., CEST' = 1 / Z. label -1 / Z ref Among them, Z label Z represents the magnetic resonance signal generated by water and CEST contrast agent at the target CEST contrast agent resonance frequency (Δω). ref The magnetic resonance signal generated by water molecules is at the resonance frequency (-Δω) opposite to that of water molecules.

[0089] 2. Obtain the relative spatial distribution map of the B1 field (B1 field) using the double-flip angle gradient echo imaging method. 1rel Let the flip angles be θ and 2θ, and the corresponding images be I1 and I2. Then B 1rel It can be obtained using the arccosine algorithm, i.e., B. 1rel =arccos(I2 / 2I1) / θ. Therefore, the actual labeled energy B 1rms '=B 1rms xB 1rel .

[0090] 3. Establish CEST and B 1rms The linear functional relationship is 1 / CEST = k / ω1 2 +b, where ω 1＝ γ·B 1rms The gyromagnetic ratio γ = 42.6 MHz / T. This is derived from the actual labeled energy B. 1rms The parameters such as k and b in the linear function model are fitted to the corresponding signal CEST.

[0091] 4. Based on the established linear function 1 / CEST=k / ω1 2 +b, then CEST=1 / (k / ω1) 2 +b) will give you B 1rms The corresponding ideal CEST signal is obtained, thereby solving the influence of B1 field inhomogeneity and achieving accurate quantification of CEST signal.

[0092] The key points and protected points of this invention are at least as follows:

[0093] 1. This invention proposes a B1 correction scheme for radio frequency fields.

[0094] 2. The linear function model correction method for radio frequency field B1 proposed in this invention has the advantages of being simple, fast, and stable, and effectively solves the limitations of existing technologies such as being cumbersome, time-consuming, having limited applicability, and being inaccurate.

[0095] 3. The radio frequency field B1 correction method proposed in this invention is beneficial for the accurate quantification of CEST signals.

[0096] Compared with the prior art, the advantages of the present invention are at least as follows:

[0097] The advantages of this invention include: (1) Compared with the analytical solution correction method based on the dual-pool Bloch-McConnell equation, the technical solution of this invention avoids the limitations of existing methods, such as being cumbersome and time-consuming, only applicable to continuous radio frequency pulse marking methods, and requiring additional information. By establishing a linear relationship between the B1 radio frequency field energy and the CEST signal, the B1 field non-uniformity correction can be achieved, which is simple and fast; (2) Compared with the polynomial fitting method based on subjective experience, the technical solution of this invention does not require the use of B1 field non-uniformity correction method. 1rel By fitting a function model to the region close to 1, it can be applied to a wider range of tissue imaging scenarios, and only two sets of B1 energy CEST data are needed to achieve B1 field inhomogeneity correction, thereby enabling accurate quantification of CEST signals.

[0098] The feasibility of this invention has been confirmed through phantom experiments. The results are as follows:

[0099] Two identical creatine biomimetic solutions with a pH of 6.8 and a concentration of 80 mM were prepared using PBS buffer. B1 radiofrequency field distribution imaging and CEST imaging were performed under a 5 T magnetic resonance field. Imaging parameters such as field of view, spatial resolution, and shimming range were kept consistent for both methods. B1 radiofrequency field distribution imaging used two flip angles of 45° and 90°, with a repetition time TR = 10 s. The calculated relative spatial distribution of the B1 field is as follows: Figure 2 As shown, the radio frequency field B1 of phantom 1 (vial 1) is significantly lower than that of phantom 2 (vial 2).

[0100] The radiofrequency pulse labeling energies for CEST imaging were 0.75 μT and 1.25 μT, with a saturation time of 3 s, a recovery time of 3 s, a frequency offset range of -3.5 to 3.5 ppm, and a step size of 0.1 ppm. The creatine CEST signal distributions corresponding to 0.75 μT and 1.25 μT are shown below. Figure 3The figure shows the spatial distribution of CEST signals of creatine phantoms at radio frequency pulse energies of 0.75 μT and 1.25 μT. When the radio frequency pulse energy is 0.75 μT, the creatine CEST signals of the two phantoms are 0.12 and 0.16, respectively; when the radio frequency pulse energy is 1.25 μT, the creatine CEST signals of the two phantoms are 0.20 and 0.25, respectively. It is evident that under the same radio frequency pulse energy, the signals of identical creatine phantoms exhibit significant differences, confirming that B1 field inhomogeneity affects the accuracy of CEST signal quantization.

[0101] Based on the constructed 1 / CEST=k / ω1 2 The +b function, derived from the actual labeled energy B. 1rms The parameters such as k and b in the linear function model are fitted to the corresponding signal CEST, and then the radio frequency field B1 is obtained after correction. 1rms The corresponding ideal CEST signal, thus resolving the influence of B1 field inhomogeneity, see [link / reference]. Figure 4 This is the B1 field correction plot based on a linear function model.

[0102] The distribution of creatine CEST signal after B1 radio frequency field correction is as follows: Figure 5 The figure shows the spatial distribution of creatine phantom CEST signals at radio frequency labeling energies of 0.75 μT and 1.25 μT after B1 radio frequency field correction. When the radio frequency pulse energy is 0.75 μT, the creatine CEST signals of the two phantoms are 0.14 and 0.16, respectively; when the radio frequency pulse energy is 1.25 μT, the creatine CEST signals of the two phantoms are 0.22 and 0.25, respectively. Compared with before B1 radio frequency field correction, at a radio frequency pulse labeling energy of 0.75 μT, the inhomogeneity of phantom 1 relative to phantom 2 decreased from 25% to 12.5%; at a radio frequency pulse labeling energy of 1.25 μT, the inhomogeneity of phantom 1 relative to phantom 2 decreased from 20% to 12%. It can be seen that the proposed B1 radio frequency field correction scheme effectively improves the influence of B1 radio frequency field inhomogeneity on CEST quantification.

[0103] Example 3

[0104] A storage medium storing a program file capable of implementing any of the above-mentioned B1 field correction methods for accurate quantification of CEST signals.

[0105] Example 4

[0106] A processor for running a program, wherein the program executes any of the above-mentioned B1 field correction methods for accurate quantification of CEST signals.

[0107] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0108] In the above embodiments of the present invention, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0109] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The system embodiments described above are merely illustrative; for example, the division of units can be a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection of units or modules may be electrical or other forms.

[0110] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0111] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0112] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part 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 to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A B1 field correction method for accurate quantification of CEST signals, characterized in that, Includes the following steps: Collect CEST data from two B1 energy markers and calculate their respective CEST' signals; Acquiring an actual energy B of a B1 field relative spatial distribution 1rms ’; establishing a functional relationship between the CEST' signal and the actual energy B 1rms coefficients of the fitted function; From the fitted function, the actual energy B after B1 field correction is calculated 1rms corresponding CEST signal; the function relationship between the established CEST' signal and the actual energy B 1rms coefficients of the fitting function include: Establishing CEST and B 1rms Functional relationship, 1 / CEST = k / ω1 2 + b, where ω1= γ· B 1rms gyromagnetic ratio γ = 42.6 MHz / T; B from the actual energy 1rms the coefficients k and b in the CEST' fitting function model The actual energy B after B1 field correction is calculated by the fitted function 1rms The corresponding CEST signal comprises: Based on the established function 1 / CEST = k / ω1 2 + b, obtain B 1rms The corresponding CEST signal, i.e. CEST = 1 / ( k / ω1 2 + b).

2. The B1 field correction method for accurate quantification of CEST signals according to claim 1, characterized in that, The acquisition of CEST data from two B1 energy markers and the calculation of their respective CEST' signals include: Two B1-energy labeled magnetic resonance signals were acquired, normalized, and the CEST' signal was calculated, where CEST' = 1 / Z. label -1 / Z ref Among them, Z label Z represents the magnetic resonance signal generated by water and CEST contrast agent at the target CEST contrast agent resonance frequency Δω. ref The main magnetic field offset correction uses conventional data preprocessing methods to represent the magnetic resonance signal generated by water molecules at -Δω relative to the resonance frequency opposite to the water molecules.

3. The B1 field correction method for accurate quantification of CEST signals according to claim 2, characterized in that, When normalizing the signal, Z = S / S0, where S is the magnetic resonance signal with radio frequency pulse marking and S0 is the magnetic resonance signal without radio frequency pulse marking.

4. The B1 field correction method for accurate quantification of CEST signals according to claim 1, characterized in that, The actual energy B1 relative spatial distribution of the B1 field is obtained. 1rms 'include: The actual energy B1 relative spatial distribution of the B1 field was obtained using the double-flip angle gradient echo imaging method. 1rms '.

5. The B1 field correction method for accurate quantification of CEST signals according to claim 4, characterized in that, The actual energy B1 field relative spatial distribution is obtained using the double-flip-angle gradient echo imaging method. 1rms 'include: The relative spatial distribution of field B1 was obtained using the double-flip-angle gradient echo imaging method. 1rel Let the flip angles be θ and 2θ, and the corresponding images be I1 and I2, then B 1rel B is obtained using the arccosine algorithm Arccos. 1rel =arccos(I² / 2I¹) / θ, actual energy B 1rms '=B 1rms xB 1rel .

6. A B1 field correction device for precise quantification of CEST signals, characterized in that, The B1 field correction method for accurate quantification of CEST signals according to any one of claims 1 to 5 is implemented; the B1 field correction device comprises: The data acquisition unit is used to acquire CEST data from two B1 energy markers and calculate their respective CEST' signals. The energy acquisition unit is used to acquire the actual energy B of the B1 field relative spatial distribution. 1rms '; Function fitting unit, used to establish the relationship between the CEST' signal and the actual energy B 1rms The functional relationship between them, and the coefficients of the fitted function; The signal calculation unit is used to calculate the actual energy B after field correction from the fitted function. 1rms The corresponding CEST signal.

7. A storage medium, characterized in that, The storage medium stores a program file capable of implementing the B1 field correction method for accurate quantification of CEST signals as described in any one of claims 1 to 5.

8. A processor, characterized in that, The processor is used to run a program, wherein the program executes the B1 field correction method for accurate quantification of CEST signals as described in any one of claims 1 to 5.

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