Lee Ju Hee, Cheong Hyunhee, Lee Seung Soo, Lee Chang Kyung, Sung Yu Sub, Huh Jae-Wan, Song Jung-A, Choe Han
From the *Department of Radiology, Center for Liver Cancer, National Cancer Center, Goyang; †Department of Radiology and Research Institute of Radiology, Asan Medical Center, Departments of ‡Biochemistry and Molecular Biology, and §Physiology and Biomedical Institute of Technology, University of Ulsan College of Medicine, Seoul, South Korea.
Invest Radiol. 2016 Aug;51(8):520-8. doi: 10.1097/RLI.0000000000000262.
The aims of this study were to demonstrate the theoretical meaning of intravoxel incoherent motion (IVIM) parameters and to compare the robustness of 2 biexponential fitting methods through magnetic resonance experiments using IVIM phantoms.
Intravoxel incoherent motion imaging was performed on a 3 T magnetic resonance imaging scanner using 15 b values (0-800 s/mm) for 4 phantoms with different area fractions of the flowing water compartment (FWC%), at the infusion flow rates of 0, 1, 2, and 3 mL/min. Images were quantitatively analyzed using monoexponential free biexponential, and segmented biexponential fitting models.
There were some inconsistent variations in Dslow with changing flow rates. The perfusion fraction, f, showed a significant positive correlation with the flow rate for both the free and segmented fitting methods (ρ = 0.838 to 0.969; P < 0.001). The fast diffusion coefficient, Dfast, had a significant positive correlation with the flow rate for segmented fitting (ρ = 0.745 to 0.969; P < 0.001), although it showed an inverse correlation with the flow rate for free fitting (ρ = -0.527 to -0.791; P ≤ 0.017). Significant positive correlations with the FWC% of the phantoms were noted for f (P = 0.510 for free fitting and P = 0.545 for segmented fitting, P < 0.001).
The IVIM model allows for an approximate segmentation of molecular diffusion and perfusion, with a minor contribution of the perfusion effect on Dslow. The f and Dfast can provide a rough estimation of the flow fraction and flow velocity. Segmented fitting may be a more robust method than free fitting for calculating the IVIM parameters, especially for Dfast.
本研究旨在阐明体素内不相干运动（IVIM）参数的理论意义，并通过使用IVIM体模的磁共振实验比较两种双指数拟合方法的稳健性。
在一台3T磁共振成像扫描仪上对4个具有不同流动水腔室面积分数（FWC%）的体模进行体素内不相干运动成像，使用15个b值（0 - 800 s/mm²），输注流速分别为0、1、2和3 mL/min。使用单指数、自由双指数和分段双指数拟合模型对图像进行定量分析。
随着流速变化，Dslow存在一些不一致的变化。灌注分数f对于自由拟合和分段拟合方法均与流速呈显著正相关（ρ = 0.838至0.969；P < 0.001）。快速扩散系数Dfast对于分段拟合与流速呈显著正相关（ρ = 0.745至0.969；P < 0.001），尽管其对于自由拟合与流速呈负相关（ρ = -0.527至 -0.791；P ≤ 0.017）。f与体模的FWC%呈显著正相关（自由拟合P = 0.510，分段拟合P = 0.545，P < 0.001）。
IVIM模型允许对分子扩散和灌注进行近似分割，灌注效应在Dslow上的贡献较小。f和Dfast可以对血流分数和血流速度进行粗略估计。在计算IVIM参数时，尤其是对于Dfast，分段拟合可能是比自由拟合更稳健的方法。
