Yablonskiy D A, Neil J J, Raichle M E, Ackerman J J
Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri 63110, USA.
Magn Reson Med. 1998 Feb;39(2):169-78. doi: 10.1002/mrm.1910390202.
It has been observed that the signal amplitude of multiplet resonances such as the 1H doublet resonance of lactate varies with pulse sequence timing when echo-driven volume selective methods such as point resolved spectroscopy are used. Herein a standard vectorial description is presented for the mechanism of this artifact, which results from the chemical shift between homonuclear scalar-coupled (i.e., J coupled) nuclei. The chemical shift causes the extent of a signal phase modulation to vary for different spatial regions of the excited voxel. This variation results in spatial interference effects that can lead to marked loss of signal intensity as well as corruption of the size and shape of the voxel from which signal is obtained. The phenomenon is substantial at an imaging field of 1.5 T and becomes especially pronounced at higher field strengths. Several strategies to avoid the artifact are provided.
据观察，当使用诸如点分辨光谱法等回波驱动体积选择方法时，多重共振的信号幅度（如乳酸的1H双峰共振）会随脉冲序列时间而变化。本文针对这种伪影的机制给出了一种标准的矢量描述，该伪影是由同核标量耦合（即J耦合）原子核之间的化学位移引起的。化学位移导致激发体素的不同空间区域的信号相位调制程度发生变化。这种变化会导致空间干涉效应，从而可能导致信号强度显著损失以及获取信号的体素的大小和形状失真。该现象在1.5T的成像场中较为显著，在更高场强下变得尤为明显。文中提供了几种避免该伪影的策略。
