Stepisnik J, Duh A, Mohoric A, Sersa I
Physics Department, University of Ljubljana, Jadranska 19.
J Magn Reson. 1999 Mar;137(1):154-60. doi: 10.1006/jmre.1998.1678.
The enhancement of magnetic resonance image intensity near impermeable boundaries can be nicely described by a new approach where the diffusional spin echo attenuation is linked to the correlation function of molecular motion. In this method the spin phase structure created by the applied gradient is considered to be a composition of plane waves with the wave vectors representing feasible momentum states of a particle in confinement. The enhancement of edges on the magnetic resonance images (MRI) comes out as a discord of plane waves due to particle motion. It results from the average of the wave phase by using the cumulant expansion in the Gaussian approximation. The acquired analytical expression describes the MRI signal space distribution where the enhancement of edges depends on the intensity and the duration of gradient sequence as well as on the length of the mean squared particle displacement in restricted geometry. This new method works well with gradients of general waveform and is, therefore, suitable for imaging sequences where finite or even modulated gradients are usually used.
通过一种新方法可以很好地描述不可渗透边界附近磁共振图像强度的增强，该方法将扩散自旋回波衰减与分子运动的相关函数联系起来。在这种方法中，由施加梯度产生的自旋相位结构被认为是平面波的组合，其中波矢表示受限粒子的可行动量状态。由于粒子运动，磁共振图像（MRI）上边缘的增强表现为平面波的不协调。它是通过在高斯近似中使用累积量展开对波相位进行平均得到的。所获得的解析表达式描述了MRI信号的空间分布，其中边缘的增强取决于梯度序列的强度和持续时间以及受限几何结构中粒子均方位移的长度。这种新方法适用于一般波形的梯度，因此适用于通常使用有限甚至调制梯度的成像序列。
