Urchuk S N, Plewes D B
Sunnybrook Health Science Centre, Department of Medical Biophysics, University of Toronto, Ont., Canada.
J Magn Reson Imaging. 1992 Jul-Aug;2(4):453-62. doi: 10.1002/jmri.1880020415.
Mechanisms of signal loss in magnetic resonance angiography were studied with a stenotic flow phantom. The results indicate that while signal loss induced by mean fluid motions is localized about the stenosis, the fluctuating component of fluid motion induces signal loss over a much larger region, primarily distal to the stenosis. For both motion components, use of gradient moment nulling (GMN) above first order was found to be an ineffective means of reducing signal loss. In contrast, shortened gradient durations were found to reduce signal loss substantially. However, though a zeroth-order gradient is generally of the shortest duration, use of a slightly longer, first-order gradient was found to be the most robust means of reducing signal loss.
利用狭窄血流模型研究了磁共振血管造影中信号丢失的机制。结果表明，虽然平均流体运动引起的信号丢失局限于狭窄部位，但流体运动的波动分量会在大得多的区域引起信号丢失，主要在狭窄部位的远端。对于这两种运动分量，发现使用高于一阶的梯度矩归零（GMN）是减少信号丢失的无效方法。相比之下，缩短梯度持续时间可显著减少信号丢失。然而，尽管零阶梯度通常持续时间最短，但发现使用稍长的一阶梯度是减少信号丢失的最有效方法。
