Wang Changqing, He Taigang, Liu Xiaoyun, Zhong Shouming, Chen Wufan, Feng Yanqiu
School of Automation Engineering, University of Electronic Science and Technology of China, Chengdu, China; School of Biomedical Engineering, Southern Medical University, Guangzhou, China.
Magn Reson Med. 2015 Feb;73(2):865-71. doi: 10.1002/mrm.25184. Epub 2014 Apr 4.
Fitting the measured decay signal to the first moment in the presence of noncentral chi noise (M(1) NCM) can correctly address the effect of noise on the effective transverse relaxation rate (R2*) relaxometry of iron loaded liver. However, this method requires intensive computation, which restricts its application to R2* mapping. This work aims to develop a rapid implementation of the M(1) NCM method for R2* mapping.
The computation of the confluent hypergeometric function in the M(1) NCM model was approximated using cubic spline interpolation with breakpoints and coefficients precalculated and stored in a look-up table (M(1) NCM-LUT). The performance of the proposed M(1) NCM-LUT method was evaluated through simulation and based on in vivo liver R2* relaxometry data.
In both simulation and in vivo studies, the maximum absolute difference between R2* maps generated by the M(1) NCM and M(1) NCM-LUT methods was nearly 10(-3) s(-1) or less, and the M(1) NCM-LUT method obtained a R2* map in approximately 1 s and achieved an acceleration of approximately five orders of magnitude.
The proposed M(1) NCM-LUT method can significantly increase the speed of the liver R2* mapping using the M(1) NCM model. This development is important in promoting application of this R2* mapping technique for tissue iron quantification.
在存在非中心卡方噪声（M(1) NCM）的情况下，将测量的衰减信号拟合到一阶矩能够正确处理噪声对铁负荷肝脏有效横向弛豫率（R2*）弛豫测量的影响。然而，该方法需要大量计算，这限制了其在R2图谱绘制中的应用。本研究旨在开发一种用于R2图谱绘制的M(1) NCM方法的快速实现。
使用三次样条插值法对M(1) NCM模型中合流超几何函数的计算进行近似，其断点和系数预先计算并存储在查找表中（M(1) NCM-LUT）。通过模拟并基于体内肝脏R2*弛豫测量数据评估所提出的M(1) NCM-LUT方法的性能。
在模拟研究和体内研究中，M(1) NCM方法和M(1) NCM-LUT方法生成的R2图谱之间的最大绝对差值均接近10^(-3) s^(-1)或更小，并且M(1) NCM-LUT方法在大约1秒内获得R2图谱，实现了约五个数量级的加速。
所提出的M(1) NCM-LUT方法能够显著提高使用M(1) NCM模型进行肝脏R2图谱绘制的速度。这一进展对于推动这种R2图谱绘制技术在组织铁定量中的应用具有重要意义。
