Method and system for detecting BPA based on CEST

Abstract

The invention discloses a method and a system for detecting BPA based on CEST. The method comprises the following steps: acquiring an improved continuous wave-planar echo chemical exchange saturation transfer sequence; scanning the test tube model of the BPA according to the improved continuous wave-planar echo chemical exchange saturation transfer sequence, and collecting chemical exchange saturation transfer data; and analyzing the signal intensity and distribution of the BPA according to the chemical exchange saturation transfer data. In view of the fact that most human tumor microenvironments are weakly acidic or acidic, a boron drug BPA signal is difficult to directly detect by a conventional method. Meanwhile, compared with a PET method, radioactive element labeling does not need to be introduced, and efficient and accurate quantitative detection and visual expression of BPA can be achieved. The method has the advantages of being simple and convenient to operate, noninvasive, high in sensitivity and specificity and the like, and a new strategy is provided for establishment of a precise boron drug concentration measurement system.

Description

Technical Field

[0001] This invention relates to the field of magnetic resonance imaging and detection technology, and in particular to a method and system for detecting BPA based on CEST. Background Technology

[0002] Boron neutron capture therapy (BNCT), as an emerging binary targeted tumor radiotherapy method, primarily utilizes boron-10 (… 10 B) The interaction between the drug and the neutron beam (thermal neutrons or hyperthermal neutrons) achieves the specific killing of tumor cells. In this process, boronophenylalanine (BPA) is the core drug in BNCT treatment, and the accuracy and sensitivity of its detection method directly affect the therapeutic effect of BNCT. However, existing methods for detecting boron drug concentration have significant limitations, such as complex operation, significant damage to biological tissues, low measurement accuracy, low specificity, and the need to introduce metals or radioactive elements that may cause adverse reactions, making it difficult to meet the needs of clinical application.

[0003] Chemical Exchange Saturation Transfer (CEST), a cutting-edge magnetic resonance molecular imaging method, primarily reflects important physiological and biochemical information of target tissues by selectively saturating exchangeable protons (such as -OH, -NH, and -NH2) on specific molecular structures and detecting the resulting changes in free water signals. Compared with traditional detection techniques, CEST technology has the following unique advantages: (i) non-invasive and radiation-free, causing no damage to biological tissues; (ii) high sensitivity and specificity, enabling accurate quantitative detection of low concentrations of BPA; (iii) providing metabolic information, which helps optimize BNCT treatment plans; (iv) imaging without the need for metal or radioactive labeling; and (v) easy integration into existing clinical MR equipment, facilitating clinical application.

[0004] Given these characteristics of the CEST method, it offers new possibilities for the real-time and accurate detection of boron drug BPA concentration, making it necessary to develop corresponding detection methods. Summary of the Invention

[0005] To overcome the problems existing in the prior art, the present invention provides a method for detecting BPA based on CEST, comprising, Obtain an improved continuous-wave-plane echo chemical exchange saturation transfer sequence; The test tube model of BPA was scanned using an improved continuous wave-plane echo chemical exchange saturation transfer sequence to collect chemical exchange saturation transfer data. The signal intensity and distribution of BPA were obtained based on the analysis of chemical exchange saturation transfer data.

[0006] Furthermore, the improved continuous wave-plane echo chemical exchange saturation transfer sequence is obtained by applying a continuous wave saturation pulse before the 90° excitation pulse of the plane echo sequence.

[0007] Furthermore, the scanning parameters include: the saturation pulse module is set to a continuous wave of 1-5s, the bias frequency range is ±5-20ppm, the saturation energy is 1.0-5.0μT, the repetition time is 5000-10000ms, the echo time is 15-50ms, and 50-100 echo trains are used; a uniform symmetrical sampling method is adopted, and the center frequencies of the saturation pulses within the scanning frequency range are uniformly sampled on both sides at a spacing of 0.1-0.5ppm to acquire a signal at a bias frequency without an applied saturation pulse.

[0008] Furthermore, the pH of the test tube model of BPA is 5.0-6.5, and the concentration of BPA is 1-50 mg / L; The test tube model of BPA was obtained by dissolving BPA and fructose in a solvent at a mass ratio of 1:1-3, followed by the addition of agarose.

[0009] Furthermore, the analysis of BPA signal intensity and distribution based on chemical exchange saturation transfer data includes, After preprocessing the chemical exchange saturated transfer data, Z-spectrum, MTRAsym spectrum and CEST pseudocolor plot were generated. The signal intensity variation of BPA was obtained by using a two-pool model asymmetric magnetization transfer rate analysis method, and the distribution characteristics of BPA were visualized based on CEST pseudo-color plot.

[0010] Furthermore, B0map and B1map are collected before scanning; Before preprocessing, the chemical exchange saturation transfer data were corrected for the B0 field and B1 field using B0map and B1map.

[0011] Furthermore, the specific method for analyzing the asymmetric magnetization transfer rate of the two-pool model is as follows: ; Where MTLRasym is the magnetization transfer rate, S(-Δω) and S(+Δω) refer to the signal strength obtained when a specific radio frequency saturation pulse is applied at the resonant frequency offset of -2.65ppm and +2.65ppm, respectively, and S0 refers to the signal strength obtained without applying a saturation pulse.

[0012] The present invention also provides a system for detecting BPA based on CEST, including a magnetic resonance imaging device, a radio frequency pulse generator, and a signal processing and analysis module; The magnetic resonance imaging device is used to generate magnetic fields and radio frequency pulses to perform magnetic resonance chemical exchange saturation transfer sequence scanning on a BPA test tube model. The radio frequency pulse generator is used to generate radio frequency saturation pulses of a specific frequency; The signal processing and analysis module is used to analyze the signal intensity and distribution of BPA based on chemical exchange saturated transfer data. The magnetic resonance imaging device also includes an improved module for acquiring an improved continuous wave-plane echo chemical exchange saturation transfer sequence.

[0013] Boron phenylalanine (BPA), as an important boron-10 carrier, plays a crucial role in BNCT treatment. Clinically, quantitative detection and visualization of BPA are mainly achieved using positron emission tomography (PET). 18 F-marked BPA ( 18 The F-BPA method is used for evaluation, but it introduces radioactive element labeling, which leads to problems such as complex synthesis, high cost, and low measurement accuracy. The Chemical Exchange Saturation Transfer (CEST) method was initially designed to detect exchangeable protons in endogenous or exogenous macromolecules at the molecular level, thereby reflecting the content and state of these macromolecules in biological tissues. It mainly uses a specific radiofrequency saturation pulse sequence to selectively saturate exchangeable protons (-OH, -NH, -NH2) on the biomolecular structure. As these protons exchange with hydrogen protons on surrounding free water molecules, the free water signal changes accordingly. By detecting and analyzing the degree of change in the free water signal, the concentration information of the target substance can be accurately reflected. According to the principle of the CEST method, as long as the molecular structure of a natural substance contains exchangeable protons (-OH, -NH, or -NH2), it can be non-invasively quantitatively detected and visualized without the need for metal substances or radioactive element labeling. BPA, as an important boron-10 carrier, is mainly an amino acid derivative prepared based on L-phenylalanine. Since its molecular structure contains exchangeable protons (-NH2), it should theoretically possess CEST properties. Therefore, this invention introduces an improved Continuous Wave-Echo Planar Imaging Chemical Exchange Saturation Transfer (CW-EPI CEST) sequence to image the exchangeable protons (-NH2) on the BPA molecular structure, thereby achieving efficient and accurate detection and visualization of BPA.

[0014] Compared with the prior art, the present invention has the following beneficial effects: Given that the tumor microenvironment in the human body is mostly weakly acidic or acidic, conventional methods are insufficient for directly detecting boron drug BPA signals. Furthermore, compared to PET methods, this invention eliminates the need for radioactive element labeling and enables efficient, accurate quantitative detection and visualization of BPA. This invention offers advantages such as ease of operation, non-invasiveness, high sensitivity, and specificity, providing a novel strategy for establishing a precise boron drug concentration measurement system. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 It shows L-phenylalanine, BPA, and 18 The structural formula of F-BPA; Figure 2 A flowchart of BPA detection based on CEST is shown in the embodiment; Figure 3 A schematic diagram illustrating the construction process of the CW-EPI CEST sequence in the embodiment is shown; Figure 4 The Z-spectrum of a test tube model of BPA at pH 6.0 and a concentration of 10 mg / mL is shown. Figure 5 The MTRRasym spectrum of a test tube model of BPA at pH 6.0 and a concentration of 10 mg / mL is shown. Figure 6 Z-spectrums of test tube models of BPA at different concentrations and pH values ​​are shown. Figure 7 The Z-spectrum of a test tube model of BPA with a concentration of 10 mg / mL at different pH values ​​is shown. Figure 8 The MTRRasym spectra of test tube models of BPA with a concentration of 10 mg / mL at different pH values ​​are shown. Figure 9 CEST pseudocolor images of test tube models of BPA with a concentration of 10 mg / mL at different pH values ​​are shown. Figure 10 The Z-spectrum of a test tube model of BPA at pH 6.0 and a concentration of 10 mg / mL is shown at different saturation energies. Figure 11The MTLRasym spectra of BPA in test tubes at pH 6.0 and a concentration of 10 mg / mL are shown at different saturation energies. Figure 12 CEST pseudocolor images of test tube models of BPA at pH 6.0 and a BPA concentration of 10 mg / mL under different saturation energies are shown. Figure 13 CEST pseudocolor images of test tube models of BPA at pH 6.0 and a BPA concentration of 10 mg / mL at different saturation times with a saturation energy of 1.5 μT are shown. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. 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 are within the scope of protection of the present invention.

[0019] Example like Figure 1 As shown, L-phenylalanine, BPA, and 18 F-BPAs are all tyrosine analogs, and their molecular structures all contain exchangeable protonated amino groups (-NH2). Based on the principle of CEST detection, these molecules should theoretically exhibit the CEST effect.

[0020] like Figure 2 As shown, a method for detecting BPA based on CEST includes the following steps: S101. An improved CW-EPI CEST sequence was designed using the VnmrJ software platform on an Agilent 7.0T small animal magnetic resonance scanner.

[0021] Echo planar imaging (EPI) sequences are a rapid imaging technique, particularly suitable for scenarios requiring dynamic and real-time imaging. This embodiment achieves accurate detection of the CEST effect by incorporating a saturation pulse module into a traditional EPI sequence. Specifically, a continuous wave saturation pulse is applied before the 90° excitation pulse of the EPI sequence. An improved CW-EPI CEST sequence is obtained through meticulous program design, compilation, and rigorous testing. The pulse width, energy, and center frequency can all be customized according to actual needs. The construction process of the CW-EPI CEST sequence is as follows: Figure 3 As shown.

[0022] S102. CEST data were collected from a test tube model of the boron drug BPA using the improved CW-EPI CEST sequence.

[0023] During data acquisition, the scanning parameters were set as follows: the saturation pulse module was set to a 2-second continuous wave, the bias frequency range was ±10ppm (i.e., ±3000Hz), the saturation energy was 2.0μT, the repetition time was 6000ms, the echo time was 29ms, and 64 echo trains were used. A uniform symmetrical sampling method was employed, with uniform sampling on both sides at a spacing of 0.2ppm between the center frequencies of the saturation pulses within the scanning frequency range. A signal at a bias frequency without applied saturation pulses was acquired (using a sampling point at 10000Hz as the unsaturated reference point). The entire scanning process will acquire 102 images with different center frequencies of the saturation pulses.

[0024] For the water imaging module, Echo Planar Imaging (EPI) technology is used to acquire signals. The repetition time (TR) is set to 6000ms to ensure image stability and clarity; the echo time (TE) is 29.46ms to optimize image contrast; the slice thickness (THK) is set to 2mm to obtain sufficient resolution; and the field of view (FOV) is 30mm×30mm to ensure complete coverage of the sample.

[0025] The test tube model of BPA was prepared as follows: BPA, as a fat-soluble borate derivative, is insoluble in water and requires fructose as a solubilizer. In this experiment, BPA and fructose were prepared in a 1:2 ratio. Appropriate weights of BPA + fructose powder were weighed and dissolved in phosphate buffer to prepare samples with concentrations of 5 mg / mL, 10 mg / mL, and 20 mg / mL, and pH values ​​of 5.2, 5.6, 6.0, and 6.4. These samples were then aliquoted into 2 mL NMR tubes, and agarose was added to fix the test tube model. When the agarose temperature dropped to 70°C and reached a non-colloidal state, it was slowly poured into the container, and the NMR tube containing the sample was inserted. After the agarose completely solidified, the BPA test tube model was complete.

[0026] The BPA test tube model was placed at the center of the magnetic field to ensure optimal magnetic field linearity and signal-to-noise ratio. Subsequently, frequency and energy corrections were performed, and axial T2-weighted anatomical images of the test tube model were acquired. The optimal slice was selected for second-order automatic shimming to ensure the water peak half-width at half-maximum (FWHM) was less than 15 Hz. To reduce the impact of B0 and B1 field inhomogeneities on the experimental results, B0map and B1map acquisitions were performed before CEST sequence acquisition, achieved through a series of parameter settings (TR 40 ms, TE 3 ms, 3.5 ms, 4 ms, slice thickness THK 2 mm, flip angle FA 15°). Finally, CEST data were acquired using the CW-EPI CEST sequence.

[0027] CEST, a novel molecular imaging method in the field of magnetic resonance imaging, works by pre-saturating exchangeable protons (such as -OH, -NH, and -NH2) in molecular structures using specific radio frequency saturation pulses. During pre-saturation, these high-energy hydrogen protons chemically exchange with low-energy hydrogen protons in surrounding free water molecules, leading to a decrease in the magnetic resonance signal intensity of free water. By measuring and analyzing this signal change, we can indirectly reveal the concentration of target tissues and important physiological and biochemical information.

[0028] To quantify the signal intensity of the CEST effect, this invention utilizes a modified CW-EPI CEST sequence to acquire three key images: one with a saturation pulse applied at a specific off-resonance frequency (S(Δω)) to the amino position of BPA; one with a saturation pulse applied at a position symmetrical to water (S(-Δω)) to eliminate nonspecific effects; and one with a pre-saturation pulse (S0) without an applied off-resonance frequency (typically acquired by applying a pre-saturation pulse with a center frequency far removed from the resonance frequencies of all molecules of interest to ensure that protons in water molecules are not saturated; in this embodiment, the frequency is set to 10000 Hz). Once these three images are obtained, the CEST effect is calculated using the asymmetric magnetization transfer ratio (MTRasym) analysis method, thereby quantifying the concentration of the target tissue.

[0029] S103 and CEST data were preprocessed and fitted using a specific algorithm to plot the Z-spectrum, MTRAsym spectrum, and CEST plot.

[0030] The raw CEST images obtained from the improved CW-EPI CEST sequence were corrected for the B0 and B1 fields using the acquired B0map and B1map. Data processing and analysis were performed on the MATLAB platform using specialized program scripts. A circular ROI (region of interest) with a diameter of approximately 5 mm, equivalent to the diameter of the NMR tube, was set. Z-spectrum, MTLRasym spectrum, and CEST pseudo-color image were plotted using the two-cell model asymmetric magnetization transfer rate method; specifically, the two-cell model consisted of a water cell with a center frequency of 0 ppm and an amino cell with a center frequency of 2.65 ppm.

[0031] The specific method for analyzing the asymmetric magnetization transfer rate in the two-pool model is as follows: ; Where MTLRasym is the magnetization transfer rate, S(-Δω) and S(+Δω) refer to the signal strength obtained when a specific radio frequency saturation pulse is applied at the resonant frequency offset of -2.65ppm and +2.65ppm, respectively, and S0 refers to the signal strength obtained without applying a saturation pulse.

[0032] The post-processing results were classified according to conditions such as concentration, pH value, saturation energy and saturation time, and the Z-spectrum, MTRAsym spectrum and CEST pseudo-color image of BPA test tube models under different conditions were plotted in the same figure.

[0033] Figure 4 and Figure 5The Z-spectrum and MTLRasym spectrum of a test tube model of BPA at pH 6.0 and a concentration of 10 mg / mL are shown. It can be seen that the solubilizing fructose exhibits a hydroxyl effect at a chemical shift polarization frequency of 1.0 ppm, while BPA exhibits an amino group effect at a chemical shift polarization frequency of 2.65 ppm.

[0034] Figure 6 The Z-spectrum of test tube models of BPA at different concentrations and pH values ​​is shown.

[0035] Figures 7-9 Z-spectrum, MTRAsym spectrum, and CEST pseudocolor plot of test tube models of BPA at a concentration of 10 mg / mL at different pH values ​​are shown. It can be seen that under acidic conditions at pH 6.0, BPA at a concentration of 10 mg / mL exhibits a significant CEST effect at a chemical shift polarization frequency of 2.65 ppm. Furthermore, significant differences in the CEST effect values ​​of BPA were observed under different pH conditions, with values ​​of 10.81%, 14.50%, 17.86%, and 6.32% at pH 5.2, 5.6, 6.0, and 6.4, respectively. In addition, the solubilizing fructose also showed a hydroxyl (-OH) effect at 1.0 ppm.

[0036] Figure 10 and Figure 11 The Z-scan and MTLRasym spectra of test tube models of BPA at pH 6.0 and a concentration of 10 mg / mL under different saturation energies are shown. It can be seen that the CEST effect value of boron drug BPA also shows an upward trend with the increase of saturation energy. Specifically, from the MTLRasym values, the CEST effect values ​​corresponding to saturation energy conditions of 0.5 μT, 1.0 μT, 1.5 μT, 2.0 μT, and 2.5 μT are 1.25%, 7.26%, 12.67%, 19.03%, and 23.85%, respectively.

[0037] Figure 12 and Figure 13 CEST pseudocolor images of test tube models of BPA with pH 6.0 and a BPA concentration of 10 mg / mL at different saturation energies and different saturation times at a saturation energy of 1.5 μT are shown. It can be clearly seen that the signal intensity of BPA changes, that is, the higher the saturation energy and the longer the saturation time, the higher the signal intensity of BPA.

[0038] S104. The signal strength change of BPA can be obtained through MTRasym value.

[0039] Through the above steps, it can be seen that the MTPRasym spectrum response of BPA at different concentrations is different at the same pH. We can first test the relationship between the MTPRasym value and concentration of the standard sample, and then test the MTPRasym value of the sample to be tested according to the above steps. Based on the relationship obtained from the standard sample, the BPA concentration of the sample to be tested can be obtained.

[0040] In summary, this invention employs a uniform sampling method. By selecting a symmetrical frequency range and applying saturation pulses of different frequencies in an incremental manner with specific step intervals, the signal difference at symmetrical frequencies on both sides of the water peak is calculated using the asymmetric magnetization transfer rate method and then normalized. This successfully yields high signal-to-noise ratio Z-spectrum, MTLRasym spectrum, and CEST pseudo-color image, thereby indirectly obtaining the actual concentration of BPA. This invention significantly reduces the interference of traditional magnetization transfer effects and other potential confounding factors, greatly improving the accuracy and reliability of quantitative results. Compared with traditional detection methods, this invention exhibits advantages such as ease of operation, non-invasiveness, high sensitivity, and specificity, providing a new strategy for establishing a precise boron drug concentration measurement system.

[0041] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting BPA based on CEST, characterized in that, include, Obtain an improved continuous-wave-plane echo chemical exchange saturation transfer sequence; The test tube model of BPA was scanned using an improved continuous wave-plane echo chemical exchange saturation transfer sequence to collect chemical exchange saturation transfer data. The signal intensity and distribution of BPA were obtained based on the analysis of chemical exchange saturation transfer data.

2. The method for detecting BPA based on CEST according to claim 1, characterized in that, The improved continuous wave-plane echo chemical exchange saturation transfer sequence is obtained by applying a continuous wave saturation pulse before the 90° excitation pulse of the plane echo sequence.

3. The method for detecting BPA based on CEST according to claim 1, characterized in that, The scanning parameters include: the saturation pulse module is set to a continuous wave of 1-5s, the bias frequency range is ±5-20ppm, the saturation energy is 1.0-5.0μT, the repetition time is 5000-10000ms, the echo time is 15-50ms, and 50-100 echo trains are used; a uniform symmetrical sampling method is adopted, and the center frequencies of the saturation pulses are uniformly sampled on both sides within the scanning frequency range at a spacing of 0.1-0.5ppm to acquire a signal at a bias frequency without an applied saturation pulse.

4. The method for detecting BPA based on CEST according to claim 1, characterized in that, The pH of the test tube model of BPA is 5.0-6.5, and the concentration of BPA is 1-50 mg / L; The test tube model of BPA was obtained by dissolving BPA and fructose in a solvent at a mass ratio of 1:1-3, followed by the addition of agarose.

5. The method for detecting BPA based on CEST according to claim 1, characterized in that, The signal intensity and distribution of BPA obtained from the analysis of chemical exchange saturated transfer data include, After preprocessing the chemical exchange saturated transfer data, Z-spectrum, MTRAsym spectrum and CEST pseudocolor plot were generated. The signal intensity variation of BPA was obtained by using a two-pool model asymmetric magnetization transfer rate analysis method, and the distribution characteristics of BPA were visualized based on CEST pseudo-color plot.

6. The method for detecting BPA based on CEST according to claim 5, characterized in that, B0map and B1map are collected before scanning; Before preprocessing, the chemical exchange saturation transfer data were corrected for the B0 field and B1 field using B0map and B1map.

7. The method for detecting BPA based on CEST according to claim 5, characterized in that, The specific method for analyzing the asymmetric magnetization transfer rate of the two-cell model is as follows: ； Where MTLRasym is the magnetization transfer rate, S(-Δω) and S(+Δω) refer to the signal strength obtained when a specific radio frequency saturation pulse is applied at the resonant frequency offset of -2.65ppm and +2.65ppm, respectively, and S0 refers to the signal strength obtained without applying a saturation pulse.

8. A system for detecting BPA based on CEST, characterized in that, Includes magnetic resonance imaging equipment, radio frequency pulse generator, and signal processing and analysis module; The magnetic resonance imaging device is used to generate magnetic fields and radio frequency pulses to perform magnetic resonance chemical exchange saturation transfer sequence scanning on a BPA test tube model. The radio frequency pulse generator is used to generate radio frequency saturation pulses of a specific frequency; The signal processing and analysis module is used to analyze the signal intensity and distribution of BPA based on chemical exchange saturated transfer data. The magnetic resonance imaging device also includes an improved module for acquiring an improved continuous wave-plane echo chemical exchange saturation transfer sequence.

Images