采用3.0T MR不同分析方法进行体外模型脂肪定量分析的价值

Comparison of different MR fat quantification methods at 3.0 T in a phantom study

目的 探讨采用3.0TMR不同分析方法进行体外模型脂肪定量分析的价值.方法 制作纯水、纯油和9个含油量（含油体积为10％～ 90％）的50 ml模型水脂模型.在3.0TMR成像系统上采用化学位移饱和成像[水选择性抑制成像（WS）、脂肪选择性抑制成像（FS）、矫正算法]和化学位移水脂分离成像[标准同反相位成像（IOP）、迭代最小二乘法非对称采集水脂分离（IDEAL）梯度回波成像和六回波梯度回波成像]方法对模型扫描,得到各扫描方法的脂肪含量评估值.采用配对t检验比较各MR测量方法评估值与实际脂肪含量的差异,并采用Pearson方法分析两者的相关性.以实际脂肪含量为标准,采用Bland-Altman散点图得到每种成像方法测量值差值的95％可信区间的一致性界限,判定MR测量脂肪含量评估值与实际脂肪含量的一致性.结果 采用WS、IDEAL梯度回波成像和六回波梯度回波成像方法测得的脂肪含量评估值分别为（49.6±28.8）％、（46.0±28.4）％和（51.0±32.0）％,与实际脂肪含量（50％）间的差异无统计学意义（t值分别为-0.186、-2.218和2.713,P值分别为0.856、0.051和0.055）;采用FS、矫正算法和IOP测得的脂肪含量评估值分别为（64.2±26.7）％、（58.9±31.9）％和（45.3±32.3）％,与实际脂肪含量差异有统计学意义（t值分别为5.168、4.273和-6.441,P均＜0.01）.各MR成像方法脂肪定量评估值与实际脂肪含量间均具有高度相关性,r值分别为0.977（FS）、0.978（矫正算法）、0.982（WS）、0.998 （IOP）、0.993（IDEAL梯度回波成像）、0.999（六回波梯度回波成像）,P均＜0.01.Bland-Altman散点图得到的每种成像方法评估值与实际值差值的95％一致性区间为：WS（-14.7％～13.8％）,FS（-3.6％～ 32.0％）,矫正算法（-4.6％～ 22.5％）,IOP（-9.4％～0.0％）,IDEAL梯度回波序列（-15.9％ ～ 7.8％）,六回波梯度回波成像（-2.0％ ～ 4.0％）.六回波梯度回波成像评估值与实际脂肪含量相关性和一致性最好.结论 在3.0TMR上对体外模型进行脂肪定量分析,化学位移水脂分离成像较化学位移饱和成像更能提供精确的脂肪定量结果.六回波梯度回波成像定量评估值最接近实际脂肪含量.

Objective To investigate the value of MR imaging methods for the quantification of fat content in a customized lipid phantom at 3.0 T.Methods Eleven homogeneous fat-water phantoms （50 ml）with fat volume percentages from 0 to 100％ were constructed with reference to Bernard＇s methods.Fat tractions of the lipid phantom were acquired using water selective saturation （WS）,fat selective saturation （FS）,in-and out-of-phase imaging （IOP）,iterative decomposition of water and fat with echo asymmetry and least-squares estimation （IDEAL） gradient echo imaging and IDEAL Quant imaging methods on a 3.0 T MRI system.For statistical comparisons,paired-sample t test,Pearson correlation test,and Bland-Ahman maps were applied.Results Evaluated fat fractions acquired by WS,IDEAL Gradient echo imaging and IDEAL Quant were （49.6±28.8）％,（46.0±28.4）％,（51.0±32.0）％,the result has no significant difference with the true fat contents（t values were-0.186,-2.218,2.713;P values were 0.856,0.051,0.055）.Evaluated fat fractions acquired by FS,corrected algorithm and IOP were （64.2±26.7）％,（58.9±31.9）％ and （45.3±32.3）％,these three kinds of methods have significant difference with the true fat contents （t values were 5.168,4.273,-6.441;P＜0.01）.All the chemical shift imaging methods correlated with the true phantom model fat fractions,r values were 0.977（FS）,0.978 （corrected algorithm）,0.982 （WS）,0.99 8（IOP）,0.993 （IDEAL Gradient echo imaging）,0.999 （IDEAL Quant） （all P＜0.01）.Each method＇s 95％ confidence interval of the mean difference acquired by Bland-Altman map was WS （-14.7％ to 13.8％）,FS （-3.6％ to 32.0％）,corrected algorithm （-4.6％ to 22.5％）,IOP（-9.4％ to 0.0％）,IDEAL gradient echo imaging （-15.9％ to 7.8％）,IDEAL Quant（-2.0％ to 4.0％）.IDEAL Quant had the best correlation and confidence with the true fat fraction.Conclusions Chemical shift imaging methods （IOP,IDEAL Gradient echo imaging,IDEAL Quant） can acquire more accurate fat quantification results than chemical saturation imaging methods （FS,Corrected algorithm,WS） in a customized lipid phantom at 3.0 T.IDEAL Quant can acquire the best fat quantification result compared with the other imaging methods.