Bashir Adil, Yablonskiy Dmitriy A
Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri 63110, USA.
Magn Reson Med. 2006 Jul;56(1):7-18. doi: 10.1002/mrm.20917.
The discrete Fourier transform (FT) is a conventional method for spatial reconstruction of chemical shifting imaging (CSI) data. Due to point spread function (PSF) effects, FT reconstruction leads to intervoxel signal leakage (Gibbs ringing). Spectral localization by imaging (SLIM) reconstruction was previously proposed to overcome this intervoxel signal contamination. However, the existence of magnetic field inhomogeneities creates an additional source of intervoxel signal leakage. It is demonstrated herein that even small field inhomogeneities substantially amplify intervoxel signal leakage in both FT and SLIM reconstruction approaches. A new CSI data acquisition strategy and reconstruction algorithm (natural linewidth (NL) CSI) is presented that eliminates effects of magnetic field inhomogeneity-induced intervoxel signal leakage and intravoxel phase dispersion on acquired data. The approach is based on acquired CSI data, high-resolution images, and magnetic field maps. The data are reconstructed based on the imaged object structure (as in the SLIM approach) and a reconstruction matrix that takes into account the inhomogeneous field distribution inside anatomically homogeneous compartments. Phantom and in vivo results show that the new method allows field inhomogeneity effects from the acquired MR signal to be removed so that the signal decay is determined only by the "natural" R2 relaxation rate constant (hence the term "natural linewidth" CSI).
离散傅里叶变换（FT）是化学位移成像（CSI）数据空间重建的传统方法。由于点扩散函数（PSF）效应，傅里叶变换重建会导致体素间信号泄漏（吉布斯振铃）。成像光谱定位（SLIM）重建先前已被提出以克服这种体素间信号污染。然而，磁场不均匀性的存在产生了额外的体素间信号泄漏源。本文证明，即使是小的场不均匀性也会在傅里叶变换和成像光谱定位重建方法中显著放大体素间信号泄漏。本文提出了一种新的CSI数据采集策略和重建算法（自然线宽（NL）CSI），该算法消除了磁场不均匀性引起的体素间信号泄漏和体素内相位色散对采集数据的影响。该方法基于采集的CSI数据、高分辨率图像和磁场图。数据基于成像对象结构（如在成像光谱定位方法中）和考虑解剖学上均匀隔室内不均匀场分布的重建矩阵进行重建。体模和体内实验结果表明，新方法能够消除采集的磁共振信号中的场不均匀性影响，从而使信号衰减仅由“自然”R2弛豫速率常数决定（因此称为“自然线宽”CSI）。
