超短回波时间成像定量评估肝脏铁过载：基于模拟、水模和活体数据比较采集和拟合方法。
Ultrashort echo time imaging for quantification of hepatic iron overload: Comparison of acquisition and fitting methods via simulations, phantoms, and in vivo data.
机构信息
Department of Diagnostic Imaging, St. Jude Children's Research Hospital, Memphis, Tennessee, USA.
Department of Biomedical Engineering, The University of Memphis, Memphis, Tennessee, USA.
出版信息
J Magn Reson Imaging. 2019 May;49(5):1475-1488. doi: 10.1002/jmri.26325. Epub 2018 Oct 25.
BACKGROUND
Current R2*-MRI techniques for measuring hepatic iron content (HIC) use various acquisition types and fitting models.
PURPOSE
To evaluate the accuracy and precision of R2*-HIC acquisition and fitting methods.
STUDY TYPE
Signal simulations, phantom study, and prospective in vivo cohort.
POPULATION
In all, 132 patients (58/74 male/female, mean age 17.7 years).
FIELD STRENGTH/SEQUENCE: 2D-multiecho gradient-echo (GRE) and ultrashort echo time (UTE) acquisitions at 1.5T.
ASSESSMENT
Synthetic MR signals were created to mimic published GRE and UTE methods, using different R2* values (25-2000 s ) and signal-to-noise ratios (SNR). Phantoms with varying iron concentrations were scanned at 1.5T. In vivo data were analyzed from 132 patients acquired at 1.5T. R2* was estimated by fitting using three signal models. Accuracy and precision of R2* measurements for UTE acquisition parameters (SNR, echo spacing [ΔTE], maximum echo time [TE ]) and fitting methods were compared for simulated, phantom, and in vivo datasets.
STATISTICAL TESTS
R2* accuracy was determined from the relative error and by linear regression analysis. Precision was evaluated using coefficient of variation (CoV) analysis.
RESULTS
In simulations, all models had high R2* accuracy (error <5%) and precision (CoV <10%) for all SNRs, shorter ΔTE (≤0.5 msec), and longer TE (≥10.1 msec); except the constant offset model overestimated R2* at the lowest SNR. In phantoms and in vivo, all models produced similar R2* values for different SNRs and shorter ΔTEs (slopes: 0.99-1.06, R > 0.99, P < 0.001). In all experiments, R2* results degraded for high R2* values with longer ΔTE (≥1 msec). In vivo, shorter and longer TE gave similar R2* results (slopes: 1.02-1.06, R > 0.99, P < 0.001) for the noise subtraction model for 25≤R2*≤2000 s . However, both quadratic and constant offset models, using shorter TE (≤4.7 msec) overestimated R2* and yielded high CoVs up to ∼170% for low R2* (<250 s ).
DATA CONCLUSION
UTE with TE ≥ 10.1 msec and ΔTE ≤ 0.5 msec yields accurate R2* estimates over the entire clinical HIC range. Monoexponential fitting with noise subtraction is the most robust signal model to changes in UTE parameters and achieves the highest R2* accuracy and precision.
LEVEL OF EVIDENCE
2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:1475-1488.
背景
目前用于测量肝脏铁含量（HIC）的 R2*-MRI 技术使用了各种采集类型和拟合模型。
目的
评估 R2*-HIC 采集和拟合方法的准确性和精密度。
研究类型
信号模拟、体模研究和前瞻性体内队列研究。
人群
共 132 例患者（58/74 例男性/女性，平均年龄 17.7 岁）。
磁场强度/序列：1.5T 上的 2D 多回波梯度回波（GRE）和超短回波时间（UTE）采集。
评估
使用不同的 R2* 值（25-2000s）和信噪比（SNR），模拟发表的 GRE 和 UTE 方法，创建了合成 MR 信号。在 1.5T 下对具有不同铁浓度的体模进行扫描。对 132 例在 1.5T 下采集的患者进行体内数据分析。通过使用三种信号模型拟合来估计 R2*。对模拟、体模和体内数据集的 UTE 采集参数（SNR、回波间隔[ΔTE]、最大回波时间[TE]）和拟合方法的 R2*测量精度和精度进行了比较。
统计学检验
通过相对误差和线性回归分析确定 R2*的准确性。使用变异系数（CoV）分析评估精度。
结果
在模拟中，所有模型在所有 SNR、较短的ΔTE（≤0.5ms）和较长的 TE（≥10.1ms）下，均具有较高的 R2准确性（误差<5%）和精度（CoV<10%）；只有在最低 SNR 下，常数偏移模型高估了 R2*。在体模和体内，所有模型在不同 SNR 和较短的ΔTE 下产生了相似的 R2*值（斜率：0.99-1.06，R>0.99，P<0.001）。在所有实验中，随着ΔTE（≥1ms）的增加，R2*值较高时，R2*结果会变差。在体内，噪声相减模型的较短和较长 TE（25≤R2*≤2000s）给出了相似的 R2*结果（斜率：1.02-1.06，R>0.99，P<0.001）。然而，对于较短的 TE（≤4.7ms），二次和常数偏移模型均高估了 R2，并且对于较低的 R2*（<250s），CoV 高达约 170%。
数据结论
TE≥10.1ms 和 ΔTE≤0.5ms 的 UTE 可在整个临床 HIC 范围内获得准确的 R2估计。使用噪声相减的单指数拟合是对 UTE 参数变化最稳健的信号模型，可实现最高的 R2准确性和精密度。
证据水平
2 技术功效：2 级。J. Magn. Reson. Imaging 2019;49:1475-1488.
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