Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO, USA.
Division of Biostatistics, Washington University School of Medicine, St. Louis, MO, USA.
Pediatr Radiol. 2022 Jul;52(8):1476-1483. doi: 10.1007/s00247-022-05352-4. Epub 2022 Apr 6.
Magnetic resonance imaging (MRI)-based liver iron quantification is the standard of care to guide chelation therapy in children at risk of hemochromatosis. T2* relaxometry is the most widely used technique but requires third-party software for post-processing. Vendor-provided three-dimensional (3-D) multi-echo Dixon techniques are now available that allow inline/automated post-processing.
The purpose of our study was to evaluate the diagnostic accuracy of a volumetric multi-echo Dixon technique using conventional T2* relaxometry as the reference standard in a pediatric and young adult population.
In this retrospective study, we queried the radiology information system to identify all MRIs performed for liver iron quantification from July 2015 to January 2020. All patients had undergone T2* relaxometry on a 1.5-tesla (T) scanner for liver iron concentration (LIC) estimation. In addition, a 3-D multi-echo Dixon was performed using Siemens Healthineers LiverLab (Erlangen, Germany). Two readers independently estimated liver R2* and T2* on the multi-echo Dixon by drawing free-hand regions of interest on the scanner-generated R2* and T2* maps. Conventional T2*-relaxometry-based LIC was the reference standard. We estimated interobserver agreement by concordance correlation coefficient (CCC). We used Bland-Altman analysis and Pearson correlation coefficient (r) to compare LIC by the two methods.
Fifty-four MRIs on 38 patients (22 females) were available for analysis. Mean patient age was 11.8 years (standard deviation [SD] 5.3 years). Reference standard LIC ranged 1.1-21.1 (median 6.8) mg/g dry weight of liver. The concordance between readers for T2* estimation using 3-D multi-echo Dixon was substantial (CCC 0.99, confidence interval 0.99-1.00). Bland-Altman plot showed that all observations were clustered around the zero bias line if the LIC average was ≤8 mg/g, and r was very strong (reader 1 r=0.93, reader 2 r=0.92, both P-values <0.001). With increasing LIC, there was a pattern of poor agreement on the Bland-Altman plot, with observations crossing the lower limits of agreement, and r was very weak (reader 1 r=0.05, P-value 0.84; reader 2 r=0.17, P-value 0.44).
Vendor-based 3-D multi-echo Dixon allows for excellent interobserver correlation in liver T2* estimation. LIC estimated by this method has a very strong correlation with conventional T2* relaxometry if liver iron overload is mild-moderate (LIC ≤8 mg/g).
基于磁共振成像（MRI）的肝脏铁定量是指导铁螯合治疗血色病高危儿童的标准。T2*弛豫率是最广泛使用的技术，但需要第三方软件进行后处理。现在可提供供应商提供的三维（3-D）多回波 Dixon 技术，允许进行在线/自动后处理。
本研究的目的是评估一种容积多回波 Dixon 技术的诊断准确性，该技术使用常规 T2*弛豫率作为参考标准，在儿科和年轻成人人群中进行评估。
在这项回顾性研究中，我们通过检索放射学信息系统来确定 2015 年 7 月至 2020 年 1 月期间所有用于肝脏铁定量的 MRI。所有患者均在 1.5T 扫描仪上进行 T2弛豫率测量，以估计肝脏铁浓度（LIC）。此外，还使用西门子健康医疗公司的 LiverLab（德国埃尔兰根）进行了 3-D 多回波 Dixon。两位读者通过在扫描仪生成的 R2和 T2图谱上绘制自由手感兴趣区，分别独立估计多回波 Dixon 上的肝脏 R2和 T2*。常规 T2*-弛豫率测定的 LIC 是参考标准。我们通过一致性相关系数（CCC）来估计观察者间的一致性。我们使用 Bland-Altman 分析和 Pearson 相关系数（r）来比较两种方法的 LIC。
38 例患者（22 例女性）的 54 次 MRI 可用于分析。患者平均年龄为 11.8 岁（标准差 [SD] 5.3 岁）。参考标准 LIC 范围为 1.1-21.1（中位数 6.8）mg/g 干重肝脏。使用 3-D 多回波 Dixon 进行 T2*估计时，两位读者之间的一致性很高（CCC 0.99，置信区间 0.99-1.00）。Bland-Altman 图显示，如果 LIC 平均值≤8mg/g，则所有观察结果均集中在零偏置线附近，且 r 值非常强（读者 1 r=0.93，读者 2 r=0.92，两者 P 值均<0.001）。随着 LIC 的增加，Bland-Altman 图上的一致性模式较差，观察结果越过了下限，r 值非常弱（读者 1 r=0.05，P 值 0.84；读者 2 r=0.17，P 值 0.44）。
基于供应商的 3-D 多回波 Dixon 允许对肝脏 T2估计进行出色的观察者间相关性。如果肝脏铁过载为轻度至中度（LIC≤8mg/g），则该方法估计的 LIC 与常规 T2弛豫率具有很强的相关性。
