MR超短回波序列在肝铁和脂肪过载情况下定量分析肝铁浓度的实验研究

Experimental study of ultra-short echo time MR imaging for quantitative analysis of iron concentration in fatty liver with liver iron overload

目的:探讨MR超短回波序列(UTE)对肝铁沉积定量分析的准确性,以及脂肪沉积对肝铁浓度定量测量的影响。方法:将63只雄性新西兰兔随机分为2组,分别用于建立单纯铁过载模型(A组,30只)和铁过载合并脂肪肝模型(B组,33只)。在3.0T磁共振仪上采用UTE序列(包含8个回波时间:0.03、0.08、0.13、0.23、0.43、0.73、1.03和2.03 ms)进行扫描,测量实验兔肝脏的R_(2)^(*)值。对兔肝组织标本采用化学法测量肝铁浓度(LIC),并采用病理方法测量肝脏的脂肪分数。采用Spearman相关性分析评估肝脏R_(2)^(*)值与LIC的相关性,并建立线性回归方程。采用协方差分析法观察肝脏脂肪分数对铁浓度测量的影响。以去铁治疗方案中采用的肝铁含量分级阈值(1.8、3.2、7.0和15.0 mg/g)为参考标准,采用受试者工作特征(ROC)曲线评价R_(2)^(*)值对不同铁过载分级的诊断效能。结果:63只新西兰兔中最终存活49只(77.8%)。UTE-R_(2)^(*)值与肝铁浓度呈显著正相关(r=0.947,P<0.0001)。协方差分析结果显示,单纯铁过载组与铁过载合并脂肪肝组之间线性回归方程的斜率无显著差异(P>0.05)。ROC曲线分析显示,肝脏R_(2)^(*)最佳截断值为623、678、1400和2050 Hz时,预测不同铁沉积程度(1.8、3.2、7.0和15.0 mg/g)的曲线下面积(AUC)分别为0.919、0.968、0.992和0.998。结论:磁共振UTE序列获取的R_(2)^(*)值能够对肝内铁浓度进行精确测量,对铁过载具有很好的分级诊断效能,尤其是对重度铁过载,且不受肝内脂肪沉积的影响。

Objective:The purposes of this study were to investigate the accuracy of ultra-short echo time(UTE)sequence MRI in quantitatively measuring liver iron accumulation and to assess the influence of fat on liver iron quantification.Methods:Sixty-three male New Zealand rabbits were divi-ded into two groups,30 in the iron overload group and 33 in the iron overload complicated with fatty liver group.All MR examinations were performed on a clinical 3.0T scanner using UTE sequence with eight TEs of 0.03,0.08,0.13,0.23,0.43,0.73,1.03 and 2.03ms.Then R_(2)^(*) values of liver were mea-sured.Liver iron concentration(LIC)of liver tissue specimens was measured by chemical method,and fat fraction were also measured by pathology.The correlation between R_(2)^(*) and LIC was evaluated by Spearman rank correlation analysis and the linear regression equations were built.The covariance analysis was used to compare the effects of fat on iron measurement.LIC grading(1.8,3.2,7.0 and 15.0mg of iron per gram of dry tissue)was referred to the clinic iron chelation thresholds.The diagnostic efficacy of UTE-R_(2)^(*) for prediction different grades of LIC was evaluated by receiver operating characteristic(ROC)curve.Results:Among 63 New Zealand rabbits,49 rabbits survived(77.8%)and underwent MR scan using UTE sequence.The UTE-R_(2)^(*) value was significantly positively correlated with the LIC(r=0.947,P<0.0001).Covariance analysis showed that there was no significant diffe-rence in the slope of the equation between the iron overload group and the iron overload complicated with fatty liver group(P>0.05),indicating that fat has no effect on iron quantification.ROC analysis showed that the best cut-off values of R_(2)^(*) for different grades of iron deposits of 1.8,3.2,7.0 and 15.0mg/g were 623,678,1400 and 2050Hz,respectively,and the areas under the curve were 0.919,0.968,0.992 and 0.998,respectively.Conclusion:The R_(2)^(*) value based on UTE sequence can accurately quantify liver iron content,especially for heavy iron deposition.At the same time,it can eliminate the influence of fat tissue on liver iron quantification.It has a good grading diagnostic performance for different grades of iron overload.