Brihuega-Moreno Oscar, Heese Frank P, Hall Laurance D
Herchel Smith Laboratory for Medicinal Chemistry, University of Cambridge School of Clinical and Veterinary Medicine, University Forvie Site, Cambridge, UK.
Magn Reson Med. 2003 Nov;50(5):1069-76. doi: 10.1002/mrm.10628.
A novel approach to optimized diffusion measurements by minimizing the Cramer-Rao lower bound (CRLB) with respect to the b-values used for diffusion measurement was investigated. The applicability of the CRLB to these measurements is shown by the close agreement between the CRLB prediction and the actual precision obtained from experimental results. Where studies using a propagation-of-errors approach have restricted the optimization of the diffusion measurement to two b-values and to specific diffusion coefficient values, the CRLB approach sets no bounds on the number of b-values and is applicable to any system. The optimal number of b-values depends on the ratio of the maximum and minimum diffusion coefficients in the sample (the D(ratio)) and on the number of acquisitions. For a D(ratio) above 6.8 the optimal number of b-values increases to three; at a D(ratio) of 21.8 it increases to four. The optimized sampling schemes for ADC measurements in a variety of representative tissues found in the human body are given. For cartilage the optimal five-point acquisition scheme requires one measurement at a b-value of 0 and four at 1036 sec mm(-2), whereas brain requires one at 0, three at 660, and one at 1987 sec mm(-2).
研究了一种通过相对于用于扩散测量的b值最小化克拉美罗下界（CRLB）来优化扩散测量的新方法。CRLB对这些测量的适用性通过CRLB预测与从实验结果获得的实际精度之间的密切一致性得以体现。在使用误差传播方法的研究中，扩散测量的优化仅限于两个b值和特定的扩散系数值，而CRLB方法对b值的数量没有限制，适用于任何系统。b值的最佳数量取决于样品中最大和最小扩散系数的比值（D(ratio)）以及采集次数。对于高于6.8的D(ratio)，b值的最佳数量增加到三个；在D(ratio)为21.8时，增加到四个。给出了人体中各种代表性组织的ADC测量的优化采样方案。对于软骨，最佳的五点采集方案需要在b值为0时进行一次测量，在1036秒毫米(-2)时进行四次测量，而对于大脑，则需要在0时进行一次测量，在660时进行三次测量，在1987秒毫米(-2)时进行一次测量。
