Cardiovascular Research Center, Cardiology, Massachusetts General Hospital, 149 13th St, Charlestown, United States, 02129, USA.
Harvard Medical School, Boston, Massachusetts, USA.
J Magn Reson Imaging. 2021 May;53(5):1432-1443. doi: 10.1002/jmri.27473. Epub 2020 Dec 31.
Diffusion-weighted MRI (DW-MRI) of the kidneys is a technique that provides information about the microstructure of renal tissue without requiring exogenous contrasts such as gadolinium, and it can be used for diagnosis in cases of renal disease and assessing response-to-therapy. However, physiological motion and large geometric distortions due to main B field inhomogeneities degrade the image quality, reduce the accuracy of quantitative imaging markers, and impede their subsequent clinical applicability.
To retrospectively correct for geometric distortion for free-breathing DW-MRI of the kidneys at 3T, in the presence of a nonstatic distortion field due to breathing and bulk motion.
Prospective.
Ten healthy volunteers (ages 29-38, four females).
FIELD STRENGTH/SEQUENCE: 3T; DW-MR dual-echo echo-planar imaging (EPI) sequence (10 b-values and 17 directions) and a T volume.
The distortion correction was evaluated subjectively (Likert scale 0-5) and numerically with cross-correlation between the DW images at b = 0 s/mm and a T volume. The intravoxel incoherent motion (IVIM) and diffusion tensor (DTI) model-fitting performance was evaluated using the root-mean-squared error (nRMSE) and the coefficient of variation (CV%) of their parameters.
Statistical comparisons were done using Wilcoxon tests.
The proposed method improved the Likert scores by 1.1 ± 0.8 (P < 0.05), the cross-correlation with the T reference image by 0.13 ± 0.05 (P < 0.05), and reduced the nRMSE by 0.13 ± 0.03 (P < 0.05) and 0.23 ± 0.06 (P < 0.05) for IVIM and DTI, respectively. The CV% of the IVIM parameters (slow and fast diffusion, and diffusion fraction for IVIM and mean diffusivity, and fractional anisotropy for DTI) was reduced by 2.26 ± 3.98% (P = 6.971 × 10 ), 11.24 ± 26.26% (P = 6.971 × 10 ), 4.12 ± 12.91% (P = 0.101), 3.22 ± 0.55% (P < 0.05), and 2.42 ± 1.15% (P < 0.05).
The results indicate that the proposed Di + MoCo method can effectively correct for time-varying geometric distortions and for misalignments due to breathing motion. Consequently, the image quality and precision of the DW-MRI model parameters improved.
2 TECHNICAL EFFICACY STAGE: 1.
弥散加权磁共振成像（DW-MRI）是一种无需外源性对比剂（如钆）即可提供肾组织微观结构信息的技术，可用于诊断肾脏疾病和评估治疗反应。然而，由于主磁场不均匀性引起的生理运动和大的几何变形会降低图像质量，降低定量成像标志物的准确性，并阻碍其随后的临床应用。
在存在因呼吸和整体运动引起的非静态失真场的情况下，对 3T 自由呼吸 DW-MRI 中的几何变形进行回顾性校正。
前瞻性。
10 名健康志愿者（年龄 29-38 岁，女性 4 名）。
磁场强度/序列：3T；DW-MR 双回波平面回波成像（EPI）序列（10 个 b 值和 17 个方向）和 T1 容积。
主观（Likert 量表 0-5）和数字（b = 0 s/mm 处 DW 图像与 T1 参考图像之间的互相关）评估失真校正。使用均方根误差（nRMSE）和参数的变异系数（CV%）评估各向异性分数扩散张量成像（DTI）和双指数模型拟合性能。
使用 Wilcoxon 检验进行统计比较。
所提出的方法将 Likert 评分提高了 1.1±0.8（P<0.05），与 T1 参考图像的互相关提高了 0.13±0.05（P<0.05），并分别降低了 IVIM 和 DTI 的 nRMSE 0.13±0.03（P<0.05）和 0.23±0.06（P<0.05）。IVIM 参数（慢扩散、快扩散、IVIM 扩散分数和平均扩散系数、DTI 各向异性分数）的 CV%降低了 2.26±3.98%（P=6.971×10-5）、11.24±26.26%（P=6.971×10-5）、4.12±12.91%（P=0.101）、3.22±0.55%（P<0.05）和 2.42±1.15%（P<0.05）。
结果表明，所提出的 Di+MoCo 方法可以有效地校正随时间变化的几何变形和呼吸运动引起的失准。因此，DW-MRI 模型参数的图像质量和精度得到了提高。
2 技术功效分期：1。
