Accuracy of multi-echo Dixon sequence in quantification of hepatic steatosis in Chinese children and adolescents

BACKGROUND Nonalcoholic fatty liver disease(NAFLD) is currently the outstanding cause of chronic liver disease in children and adolescents, especially in overweight and obese groups. Liver biopsy is the reference standard to diagnose NAFLD but invasive, thus it is not the best choice in clinical diagnosis and follow-up.Magnetic resonance(MR) is widely used in clinical trials to noninvasively quantify liver fat content in adults and children in foreign countries. While currently, it is rarely used in Chinese children and adolescents. We postulated that quantifying hepatic steatosis by MR could be extended to children and adolescents in China.AIM To investigate the accuracy of MR imaging(MRI) in quantifying liver fat with MR spectroscopy(MRS) as a reference. A secondary goal was to assess the prevalence of NAFLD in overweight and obese Chinese children and adolescents.METHODSThere were 86 children and adolescents enrolled in this study, including 65 overweight and obese children and 21 healthy children. The participants underwent MRI and MRS. MRI and MRS were performed using multi-echo Dixon and HISTO sequences, respectively, to calculate hepatic proton density fat fraction(PDFF). Hepatic steatosis was diagnosed using MRS-PDFF > 5% as the threshold. Spearman's analysis was used to evaluate the correlation between MRI and MRS. The agreement between these two methods was assessed by BlandAltman analysis.RESULTS The MRI-PDFF in the MRS region of interest and the entire liver was 9.9% ±10.3% with a range of 0.3%-39.9%, and 10.6% ± 9.4% with a range of 1.9%-38.9%,respectively. The MRS-PDFF was 9.1% ± 10.0%, with a range of 0.5%-37.8%. The incidence of hepatic steatosis detected by MRS-PDFF was 46.5%(40/86) of all participants, all of whom belonged to the overweight and obese group.Spearman's analysis indicated an excellent correlation between multi-echo Dixon and MRS(r > 0.9, P < 0.01). Bland-Altman analysis also demonstrated a good agreement between these two methods.CONCLUSION Multi-echo Dixon shows an excellent correlation and agreement with MRS in quantifying liver fat content and could be a potential tool to detect hepatic steatosis in Chinese children and adolescents.

R2^(*) value derived from multi-echo Dixon technique can aid discrimination between benign and malignant focal liver lesions

BACKGROUND R2^(*)estimation reflects the paramagnetism of the tumor tissue,which may be used to differentiate between benign and malignant liver lesions when contrast agents are contraindicated.AIM To investigate whether R2^(*)derived from multi-echo Dixon imaging can aid differentiating benign from malignant focal liver lesions(FLLs)and the impact of 2D region of interest(2D-ROI)and volume of interest(VOI)on the outcomes.METHODS We retrospectively enrolled 73 patients with 108 benign or malignant FLLs.All patients underwent conventional abdominal magnetic resonance imaging and multi-echo Dixon imaging.Two radiologists independently measured the mean R2^(*)values of lesions using 2D-ROI and VOI approaches.The Bland-Altman plot was used to determine the interobserver agreement between R2^(*)measurements.Intraclass correlation coefficient(ICC)was used to determine the reliability between the two readers.Mean R2^(*)values were compared between benign and malignant FFLs using the nonparametric Mann-Whitney test.Receiver operating characteristic curve analysis was used to determine the diagnostic performance of R2^(*)in differentiation between benign and malignant FFLs.We compared the diagnostic performance of R2^(*)measured by 2D-ROI and VOI approaches.RESULTS This study included 30 benign and 78 malignant FLLs.The interobserver reproducibility of R2^(*)measurements was excellent for the 2D-ROI(ICC=0.994)and VOI(ICC=0.998)methods.Bland-Altman analysis also demonstrated excellent agreement.Mean R2^(*)was significantly higher for malignant than benign FFLs as measured by 2D-ROI(P<0.001)and VOI(P<0.001).The area under the curve(AUC)of R2^(*)measured by 2D-ROI was 0.884 at a cut-off of 25.2/s,with a sensitivity of 84.6%and specificity of 80.0%for differentiating benign from malignant FFLs.R2^(*)measured by VOI yielded an AUC of 0.875 at a cut-off of 26.7/s in distinguishing benign from malignant FFLs,with a sensitivity of 85.9%and specificity of 76.7%.The AUCs of R2^(*)were not significantly different between the 2D-ROI and VOI methods.CONCLUSION R2^(*)derived from multi-echo Dixon imaging whether by 2D-ROI or VOI can aid in differentiation between benign and malignant FLLs.

Liver fat accumulation measured by high-speed T2-corrected multiecho magnetic resonance spectroscopy can predict risk of cholelithiasis

BACKGROUND Liver fat accumulation is associated with increased cholesterol synthesis and hypersecretion of biliary cholesterol,which may be related to the development of cholelithiasis.AIM To investigate whether liver fat accumulation measured by high-speed T2-corrected multi-echo magnetic resonance spectroscopy(MRS)is a risk factor for cholelithiasis.METHODS Forty patients with cholelithiasis and thirty-one healthy controls were retrospectively enrolled.The participants underwent high-speed T2-corrected multi-echo single-voxel MRS of the liver at a 3T MR scanner.The proton density fat fraction(PDFF)and R2 value were calculated.Serum parameters and waist circumference(WC)were recorded.Spearman’s correlation analysis was used to analyze the relationship between PDFF,R2,and WC values.Multivariate logistic regression analysis was carried out to determine the significant predictors of the risk of cholelithiasis.Receiver operating characteristic curve(ROC)analysis was used to evaluate the discriminative performance of significant predictors.RESULTS Patients with cholelithiasis had higher PDFF,R2,and WC values compared with healthy controls(5.8%±4.2%vs 3.3%±2.4%,P=0.001;50.4±24.8/s vs 38.3±8.8/s,P=0.034;85.3±9.0 cm vs 81.0±6.9 cm,P=0.030;respectively).Liver iron concentration extrapolated from R2 values was significantly higher in the cholelithiasis group(2.21±2.17 mg/g dry tissue vs 1.22±0.49 mg/g dry tissue,P=0.034)than in the healthy group.PDFF was positively correlated with WC(r=0.502,P<0.001)and R2(r=0.425,P<0.001).Multivariate logistic regression analysis showed that only PDFF was an independent risk factor for cholelithiasis(odds ratio=1.79,95%CI:1.22-2.62,P=0.003).ROC analysis showed that the area under the curve of PDFF was 0.723 for discriminating cholelithiasis from healthy controls,with a sensitivity of 55.0%and specificity of 83.9%when the cut-off value of PDFF was 4.4%.CONCLUSION PDFF derived from high speed T2-corrected multi-echo MRS can predict the risk of cholelithiasis.

植物细胞壁纳米结构与纳米纤维素的化学纯化处理结合机械解纤法制备

植物中含有自然界中储量最为丰富的天然高分子-纤维素.植物具有多层级结构,在微观层面由细胞构成.细胞的主体物质存在于细胞壁中,主要以纤维素纳米纤丝-基体复合结构形式存在,这种结构对植物的性能和功能起到了至关重要的作用.采用化学纯化处理结合机械解纤策略,可以将细胞壁内部起支撑作用的纳米纤维素解离出来.纳米纤维素展现出一维纳米纤维结构、高结晶度以及优异的力学性能和热性能,在许多领域均展现出巨大的应用潜力.本文主要介绍我们课题组近几年对植物多层级结构、细胞特征、细胞壁生物合成以及细胞壁纳米结构的研究和思考,总结了在植物纳米纤维素化学纯化处理结合机械解纤法制备方面的研究进展,并对其存在的问题以及今后重点研究方向进行了总结和展望.