Objective:To explore the clinical application value of pre-breathing mode in double-low imaging of 320-slices computed tomography(CT)for pulmonary artery.Methods:A total of 100 patients who underwent CT pulmonary angiography(CTPA)for suspected pulmonary embolism(PE)in Liuzhou People's Hospital from July 2021 to September 2022 were prospectively selected as the research subjects and they were randomly divided into observation group and control group,with 50 cases in each group.The patients of the control group adopted conventional breathing mode(the breathing password was activated after reaching the threshold,and the scan was triggered after 6 s),while the patients of the observation group adopted the pre-breathing mode(the breathing password was activated after 1 or 2 seconds,and the scan was triggered after reaching the threshold).Both two groups adopted double low-technique scan of 320 slices CT.The differences in delay time,radiation dose,the points of subjective and objective image quality,and other indicators were compared between the two groups.Results:The volume CT dose index(CTDIvol),dose length product(DLP),effective dose(ED)and delay time of the observation group were significantly lower than those of the control group(t=76.230,30.225,12.282,7.088,P<0.05),respectively.The comparison of the subjective points of image qualities between the two groups indicated that there were 25 cases with 5 points,23 cases with 4 points and 2 cases with 3 points in the observation group,and there were 21 cases with 5 points,26 cases with 4 points and 3 cases with 3 points in the control group.There was no significant difference in the averagely subjective points of image qualities between two groups(P>0.05).The signal-to-noise ratio(SNR)and signal to noise ratio(CNR)of the observation group were significantly lower than those of the control group,and the noise level(SD)of the observation group was significantly higher than that of the control group(t=25.441,23.886、11.426,P<0.05),respectively.The CT values of the artery trunk of right pulmonary,artery branch of right pulmonary,artery trunk of left pulmonary and artery branch of left pulmonary in the observation group were significantly higher than those in the control group(t=2.256,2.225,2.042,2.277,P<0.05),respectively.Conclusion:The pre-breathing mode can effectively improve CTPA image quality,and reduce radiation dose and the dosage of contrast agent,which clinical application effect is significant.It is worth learning.

OBJECTIVE：To establish pre -column derivatization-HPLC fingerprint of Polyporus polysaccharide ，and to determine the contents of main monosaccharide components ，so as to provide reference for quality evaluation of Polyporus umbellatus. METHODS ：Polyporus polysaccharide was extracted with boiling water and precipitated by ethanol and deproteinized by Sevage from 11 batches of P. umbellatus from different producing areas. The samples were firstly hydrolyzed with trifluoro-acetic acid （TFA）and then derivatized by 1-phenyl-3-methyl-5-pyrazolone（PMP）. HPLC analysis was then conducted. The determination was carried out on HypersiL BDS C 18 column with mobile phase composed of 0.1 mol/L phosphate buffer （pH 6.84）-acetonitrile（84∶16，V/V）by gradient elution at the flow rate of 1.0 mL/min. The detection wavelength was set at 254 nm， and column temperature was 30 ℃. The sample size was 20 µL. The similarity of 11 batches of Polyporus polysaccharide was evaluated by using TCM Chromatographic Fingerprint Similarity Evaluation System （2012A edition ），and the contents of main monosassharide components were detected. The peak was identified by comparing with the reference substance ，and cluster analysis was performed by using SPSS 23.0 software. RESULTS ：In HPLC fingerprints of the 11 batches of samples ，3 common peaks were identified ，namely mannose ，glucose and galactose. The similarity of all samples was above 0.94. Cluster analysis classified 11 batches of samples into three categories. S 1-S6，and S 8 were grouped into category 1；S7，S10 and S 11 were grouped into category 2；S9 was individually grouped into one category. Results of content determination showed that the contents of mannose ranged from 1.571 to 8.771 mg/g；those of glucose ranged from 26.072 to 132.194 mg/g，and those of galactose ranged from 3.420 to 36.593 mg/g. CONCLUSIONS ：Established pre-column derivatization HPLC fingerprints can provide reference for quality evaluation of P. umbellatus . The monosaccharide composition of different batches of Polyporus polysaccharide is the same ；there is no significant correlation between fingerprint characteristic peak and the origin of herbs ；there is significant difference in the content of monosaccharide of P. umbellatus .