Freiman Moti, Voss Stephan D, Mulkern Robert V, Perez-Rossello Jeannette M, Callahan Michael J, Warfield Simon K
Moti Freiman, Computational Radiology Laboratory, Department of Radiology, Boston Children's Hospital, Harvard Medical School, 300 Longwood Avenue, Boston Massachusetts 02115, USA.
Med Phys. 2012 Aug;39(8):4832-9. doi: 10.1118/1.4736516.
To assess the optimal b-values range for perfusion-insensitive apparent diffusion coefficient (ADC) imaging of abdominal organs using short-duration DW-MRI acquisitions with currently available ADC estimation methods.
DW-MRI data of 15 subjects were acquired with eight b-values in the range of 5-800 s∕mm(2). The reference-standard, a perfusion insensitive, ADC value (ADC(IVIM)), was computed using an intravoxel incoherent motion (IVIM) model with all acquired diffusion-weighted images. Simulated DW-MRI data was generated using an IVIM model with b-values in the range of 0-1200 s∕mm(2). Monoexponential ADC estimates were calculated using: (1) Two-point estimator (ADC(2)); (2) least squares three-point (ADC(3)) estimator and; (3) Rician noise model estimator (ADC(R)). The authors found the optimal b-values for perfusion-insensitive ADC calculations by minimizing the relative root mean square error (RRMS) between the ADC(IVIM) and the monoexponential ADC values for each estimation method and organ.
Low b-value = 300 s∕mm(2) and high b-value = 1200 s∕mm(2) minimized the RRMS between the estimated ADC and the reference-standard ADC(IVIM) to less than 5% using the ADC(3) estimator. By considering only the in vivo DW-MRI data, the combination of low b-value = 270 s∕mm(2) and high b-value of 800 s∕mm(2) minimized the RRMS between the estimated ADC and the reference-standard ADC(IVIM) to <7% using the ADC(3) estimator. For all estimators, the RRMS between the estimated ADC and the reference standard ADC correlated strongly with the perfusion-fraction parameter of the IVIM model (r = [0.78-0.83], p ≤ 0.003).
The perfusion compartment in DW-MRI signal decay correlates strongly with the RRMS in ADC estimates from short-duration DW-MRI. The impact of the perfusion compartment on ADC estimations depends, however, on the choice of b-values and estimation method utilized. Likewise, perfusion-related errors can be reduced to <7% by carefully selecting the b-values used for ADC calculations and method of estimation.
使用当前可用的ADC估计方法，通过短时间的DW-MRI采集来评估腹部器官灌注不敏感表观扩散系数（ADC）成像的最佳b值范围。
对15名受试者进行DW-MRI数据采集，b值范围为5-800 s∕mm²，共8个b值。使用体素内不相干运动（IVIM）模型，利用所有采集的扩散加权图像计算参考标准值，即灌注不敏感的ADC值（ADC(IVIM)）。使用IVIM模型生成b值范围为0-1200 s∕mm²的模拟DW-MRI数据。使用以下方法计算单指数ADC估计值：（1）两点估计器（ADC(2)）；（2）最小二乘三点（ADC(3)）估计器；（3）莱斯噪声模型估计器（ADC(R)）。作者通过最小化每种估计方法和器官的ADC(IVIM)与单指数ADC值之间的相对均方根误差（RRMS），找到了灌注不敏感ADC计算的最佳b值。
使用ADC(3)估计器时，低b值 = 300 s∕mm²和高b值 = 1200 s∕mm²可将估计的ADC与参考标准ADC(IVIM)之间的RRMS最小化至小于5%。仅考虑体内DW-MRI数据时，低b值 = 270 s∕mm²和高b值800 s∕mm²的组合使用ADC(3)估计器可将估计的ADC与参考标准ADC(IVIM)之间的RRMS最小化至<7%。对于所有估计器，估计的ADC与参考标准ADC之间的RRMS与IVIM模型的灌注分数参数密切相关（r = [0.78 - 0.83]，p≤0.003）。
DW-MRI信号衰减中的灌注部分与短时间DW-MRI的ADC估计中的RRMS密切相关。然而，灌注部分对ADC估计的影响取决于所使用的b值和估计方法的选择。同样，通过仔细选择用于ADC计算的b值和估计方法，与灌注相关的误差可降低至<7%。
