Optimization Of 2D-APT Imaging And Evaluation Of Its Consistency With 3D-APT Imaging On Brain Tumors

Objective:To explore the value of different combinations of saturation radiofrequency（RF）pulse power and duration for improved 2D amide proton transfer（APT）imaging;and further to explore the difference in image quality and the consistency in quantitative values measured by 2D-APT and 3D-APT imaging on brain tumors.Materials and Methods:A total of 30 subjects（11 males,mean age:54.70±11.92years old）were scanned using a 3.0 T MR scanner,the scan sequences included T1weighted imaging（T1WI）,T2 weighted imaging（T2WI）,contrast-enhanced T1WI and2D-APT with different saturation schemes.Two observers with more than 3 years of diagnostic experience evaluated the 2D-APT images based on the Likert quintile.The APT values of the three regions of interest（ROI）in the tumor core,perigma edema（if exist）and the contralateral normal white matter region were measured separately.4positions were placed in each region for data measurement,and the averaged value of the4 positions was taken as the APT value of the ROI.The consistency of qualitative evaluation and quantitative measurements by the two observers were tested using Intraclass Correlation Coefficient（ICC）and Kappa.The Friedman or spearman test was used to evaluated the differences in MTR_asym,△MTR_asym and subjective scores among different combinations of saturation powers and durations for 2D-APT.The correlation between MTR_asym（T）and Ki-67 expression evaluated by the pearson correlation coefficient.A total of 29 subjects（7 males,mean age:54.90±13.11 years old）were scanned using a 3.0 T MR scanner,the MR scans included 2D-APT and 3D-APT imaging as well as the conventional imaging sequences.APT images were subjectively evaluated by two radiologists with more than 3 years of diagnostic experience according to the Likert Quintile,and MTR_asym values were measured on 2D-APT and 3D-APT images,respectively,at the tumor core,peritumorous edema area（if exist）,and the contralateral normal white matter area.The ICC and Kappa analysis were used to assess the consistency of quantitative measurement and subjective scores,respectively,between the two observers,and represented by Bland-Altman diagram.The differences of MTR_asym（T）,MTRasym（E）,MTRasym（CNAWM）,△MTRasym（T-C）,△MTRasym（E-C）and the contrast to noise ratio（CNR）measured from 2D-APT and 3D-APT images were compared by paired sample t test or Wilcoxon rank test,and the subjective score of image quality was compared by Mann-Whitney U test.The correlation of MTR_asym（T）with Ki-67 expression was analyzed by the pearson or spearman correlation coefficient.Results:（1）The measurement data and the score of the two observers were in good agreement（ICC:0.942～0.992,Kappa:0.778）.Significant differences in MTR_asym（T）,MTRasym（E）,MTRasym（CNAWM）,△MTRasym（T-C）,△MTRasym（E-C）,and subjective scores were between between different saturation regimens（p<0.05）.When the RF pulse saturation power and duration were set as 2.0μT and 2.0 s,the MTR_asym（T）,△MTR_{asym（T-C）}values and subjective scores were shown to be the highest;when the RF pulse saturation power was 2.0μT and the duration was 1.6 s,the MTR_asym（E）was the highest;and MTR_{asym（CNAWM）}was the highest when the RF pulse saturation power was 2.0μT and the duration was 0.8 s;when the saturation power was 1.0μT for a duration of 0.8 s,the MTR_{asym（E-C）}value was the highest.pearson results showed that MTR_asym（T）were positively correlated with the Ki-67 index[（21.65±3.28）%]at the saturation power of 2.0μT and duration of 2.4 s,2.0 s,1.6 s,and 1.2 s,respectively.（2）The measurement data and the score of the two observers were in good agreement（ICC:0.767-0.998,Kappa:0.765-0.778）.The t-test and Wilcoxon rank test of paired samples showed no significant difference of MTRasym（T）,MTRasym（E）,MTRasym（CNAWM）,△MTRasym（T-C）,and△MTRasym_（E-C）measured by 2D-APT and 3D-APT sequences（p>0.05）;the Mann-Whitney U test showed that the subjective scores of 2D-APT images was higher than those of 3D-APT（p<0.05）;pearson results showed that MTR_asym（T）measured by 2D-APT and 3D-APT was positively correlated with Ki-67 index[（19.18±2.50）%]（r=0.524,P=0.031;r=0.513,P=0.035）.The Bland-Altman diagram showed good consistency of MTR_asym（T）,△MTR_{asym（T-C）},and CNR values etc.for 2D-APT and 3D-APT images.Conclusion:The saturation power of 2.0μT and duration of 2.0 s for 2D-APT imaging were clinically recommended for brain tumor imaging.2D-APT and 3D-APT showed good consistency on brain tumor imaging,and the MTR_asym values measured by both sequences can better reflect the proliferation ability of tumor cells.