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Objective:To analyze the influence of magnetic field on the proton beam delivery and dose distribution, and develop a correction method for the Bragg peak (BP) shift under the vertical magnetic field, providing reference for the dose calculation and beam delivery of MRI-guided proton therapy.Methods:Monte Carlo (MC) simulation was used to study the dose distribution of the proton beam in the water phantom under the magnetic field. The BP location was corrected by the method of" angle correction+ energy correction" , and the correction parameters were calculated by the analytical formula based on the simulation data.Results:The magnetic field caused the dose distortion and shift of BP location. The shift degree was increased with the increase of field strength and initial energy. Compared with MC simulation, the result of calculating proton deflection in the air by the analytical method yielded a deviation within 0.2%. Based on the simulation data and calculation formulas, the correction parameters under different conditions could be calculated within 1 s by using the MATLAB programming. The calculation results showed that the air layer with magnetic field, isocenter depth, irradiation direction exerted different influence on the correction parameters. After correction, the BP location was basically consistent with the expected (offset ≤0.2 mm).Conclusions:The BP shift under the vertical magnetic field can be effectively corrected by " the angle correction+ energy correction" method. The correction parameters under different conditions can be quickly and accurately calculated by the calculation formulas based on simulation data.
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OBJECTIVE：To e stablish a method for simultaneous determination of 7 constituents in Xiao ’er jinqiao granules . METHODS：QAMS method was adopted. The determination was performed on Lubex Kromasil C 18 column with mobile phase consisted of acetonitrile- 0.1％ phosphoric acid solution （gradient elution ）. The detection wavelength was set at 326 nm，the flow rate was 1.0 mL/min. The column temperature was 40 ℃，and sample size was 10 µL. Using chlorogenic acid as the internal reference，the relative correction factors （RCF）of neochlorogenic acid ，cryptochlorogenic acid ，forsythiaside A ，isochlorogenic acid B ，isochlorogenic acid A and isochlorogenic acid C were calculated. The effects of different chromatogram system ， chromatogram column ，the ratio of mobile phase ，flow rate and column temperature on RCF were investigaten. According to the two-point correction method combined with the relative retention time correction of the components to be tested ，the peak location was carried out. The contents of 7 components were determined by QAMS and SCM respectively and then compared. RESULTS： The linear range of neochlorogenic acid ，chlorogenic acid ，cryptochlorogenic acid ，forsythoside A ，isochlorogenic acid B ，isochlorogenic acid A ，isochlorogenic acid C were 9.27-92.70，37.36-373.60，13.02-130.20，7.15-71.50，4.56-45.60，6.32-63.20，14.69-146.90 µg/mL （r≥0.999 7）. The limits of quantification were 1.38，1.41，1.40，1.99，1.10，1.17，1.10 ng，respectively；and the limits of detection were 0.41，0.42，0.42，0.60，0.33，0.35，0.33 ng，respectively. RSDs of precision ，repeatability and stability tests were all less than 2％；average recoveries were 98.28％-99.15％ （RSD＜2.0％ ， n＝9）. RCFs of neochlorogenic acid ， （No.2013LZLY-K61） cryptochlorogenic acid ，forsythiaside A ，isochlorogenic acid B，isochlorogenic acid A and isochlorogenic acid C relative to xinyuliang@stu.cqmu.edu.cn chlorogenic acid were 0.995，1.007，0.580，1.243，1.252 and 1.247，respectively. RSDs of RCFs were all lower than 3％ under different chromatogram conditions. Absolute value of relative error between the relative retention time of components to be tested predicted by two-point correction combined with relative retention time correction and measured value was less than 2％. The contents measured by QAMS were 2.790-3.416， 14.526-17.907，3.763-4.531，1.625-1.982，1.087-1.523，1.434-2.219，3.631-5.078 mg/g；the contents measured by SCM method were 2.811-3.438，14.512-17.893，3.739-4.508，1.656-2.012，1.108-1.544，1.460-2.245，3.597-5.045 mg/g；relative errors of the two methods were within ±2％. CONCLUSIONS ：Two-point correction method combined with relative retention time correction can accurately locate the peaks of each constituent ；established QAMS method is simple ，rapid，accurate and reliable ，it can be used for simultaneous determination of 7 constituents in Xiao ’er jinqiao granules.
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Objective To develop a fast shimming method for permanent magnet MRI system. Methods Peak location method (PLM) was improved by calculating the eddy current effect, and the time deviation was replaced by their phase to increase the precision. Results Experiment showed that the new method took less than 45 s, which was 3 times faster than conventional method while providing the same homogeneity. The result of PLM satisfied the requirement of homogeneity. Conclusion This new method can significantly improve the homogeneity in a short time and satisfy further fast pulse sequence development on 0.5T permanent magnet MRI system, which can be generalized for any permanent magnet first order shimming.