骨骼肌肉中的钠定量：笛卡尔梯度回波和径向超短回波时间 Na MRI 技术的比较。

BACKGROUND: Clinical magnetic resonance imaging (MRI) studies often use Cartesian gradient-echo (GRE) sequences with ~2-ms echo times (TEs) to monitor apparent total sodium concentration (aTSC). We compared Cartesian GRE and ultra-short echo time three-dimensional (3D) radial-readout sequences for measuring skeletal muscle aTSC. METHODS: We retrospectively evaluated 211 datasets from 112 volunteers aged 62.3 ± 12.1 years (mean ± standard deviation), acquired at 3 T from the lower leg. For Na MRI acquisitions, we used a two-dimensional Cartesian GRE sequence and a density-adapted 3D radial readout sequence with cuboid field-of-view (DA-3D-RAD-C). We calibrated the Na MR signal using reference tubes either with or without agarose and subsequently performed a relaxation correction. Additionally, we employed a six-echo H GRE sequence and a multi-echo spin-echo sequence to calculate proton density fat fraction (PDFF) and water T2. Paired Wilcoxon signed-rank test, Cohen d for paired samples, and Spearman correlation were used. RESULTS: Relaxation correction effectively reduced the differences in muscle aTSC between the two acquisition and calibration methods (DA-3D-RAD-C using NaCl/agarose references: 20.05 versus 19.14 mM; d = 0.395; Cartesian GRE using NaCl/agarose references: 19.50 versus 18.82 mM; d = 0.427). Both aTSC of the DA-3D-RAD-C and Cartesian GRE acquisitions showed a small but significant correlation with PDFF as well as with water T2. CONCLUSIONS: Different Na MRI acquisition and calibration approaches affect aTSC values. Applying relaxation correction is advised to minimize the impact of sequence parameters on quantification, and considering additional fat correction is advisable for patients with increased fat fractions. RELEVANCE STATEMENT: This study highlights relaxation correction's role in improving sodium MRI accuracy, paving the way for better disease assessment and comparability of measured sodium signal in patients. KEY POINTS: • Differences in MRI acquisition methods hamper the comparability of sodium MRI measurements. • Measured sodium values depend on used MRI sequences and calibration method. • Relaxation correction during postprocessing mitigates these discrepancies. • Thus, relaxation correction enhances accuracy of sodium MRI, aiding its clinical use.

背景：临床磁共振成像（MRI）研究常采用笛卡尔梯度回波（GRE）序列，回波时间（TE）约为 2ms，以监测表观总钠浓度（aTSC）。我们比较了笛卡尔 GRE 和超短回波时间三维（3D）径向读取序列在测量骨骼肌 aTSC 方面的应用。

方法：我们回顾性评估了 112 名志愿者（年龄 62.3±12.1 岁）小腿在 3T 下获得的 211 个数据集。在 Na MRI 采集时，我们使用二维笛卡尔 GRE 序列和带有立方视场（DA-3D-RAD-C）的密度自适应 3D 径向读取序列。我们使用带有或不带有琼脂糖的参考管对 Na 磁共振信号进行了校准，随后进行了弛豫校正。此外，我们还采用了六个回波 H GRE 序列和多回波自旋回波序列来计算质子密度脂肪分数（PDFF）和水 T2。采用配对 Wilcoxon 符号秩检验、配对样本 Cohen d 和 Spearman 相关分析。

结果：弛豫校正有效地降低了两种采集和校准方法之间肌肉 aTSC 的差异（使用 NaCl/琼脂糖参考的 DA-3D-RAD-C：20.05 与 19.14mM；d=0.395；使用 NaCl/琼脂糖参考的笛卡尔 GRE：19.50 与 18.82mM；d=0.427）。DA-3D-RAD-C 和笛卡尔 GRE 采集的 aTSC 均与 PDFF 以及水 T2 呈小但显著的相关性。

结论：不同的 Na MRI 采集和校准方法会影响 aTSC 值。建议应用弛豫校正以最小化序列参数对定量的影响，并建议对脂肪分数增加的患者进行额外的脂肪校正。

重要性声明：本研究强调了弛豫校正在提高钠 MRI 准确性方面的作用，为更好地评估疾病和比较患者测量的钠信号铺平了道路。

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