Bar-Shir Amnon, Cohen Yoram
School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
Magn Reson Imaging. 2008 Jul;26(6):801-8. doi: 10.1016/j.mri.2008.01.051. Epub 2008 May 16.
In recent years, diffusion tensor imaging (DTI) and its variants have been used to describe fiber orientations and q-space diffusion MR was proposed as a means to obtain structural information on a micron scale. Therefore, there is an increasing need for complex phantoms with predictable microcharacteristics to challenge different indices extracted from the different diffusion MR techniques used. The present study examines the effect of diffusion pulse sequence on the signal decay and diffraction patterns observed in q-space diffusion MR performed on micron-scale phantoms of different geometries and homogeneities. We evaluated the effect of the pulse gradient stimulated-echo, the longitudinal eddy current delay (LED) and the bipolar LED (BPLED) pulse sequences. Interestingly, in the less homogeneous samples, the expected diffraction patterns were observed only when diffusion was measured with the BPLED sequence. We demonstrated the correction ability of bipolar diffusion gradients and showed that more accurate physical parameters are obtained when such a diffusion gradient scheme is used. These results suggest that bipolar gradient pulses may result in more accurate data if incorporated into conventional diffusion-weighted imaging and DTI.
近年来，扩散张量成像（DTI）及其变体已被用于描述纤维取向，并且提出了q空间扩散磁共振成像作为获取微米尺度结构信息的一种手段。因此，越来越需要具有可预测微观特征的复杂体模来检验从不同扩散磁共振技术中提取的不同指标。本研究考察了扩散脉冲序列对在不同几何形状和均匀性的微米尺度体模上进行的q空间扩散磁共振成像中观察到的信号衰减和衍射图案的影响。我们评估了脉冲梯度刺激回波、纵向涡流延迟（LED）和双极LED（BPLED）脉冲序列的效果。有趣的是，在均匀性较差的样本中，只有当使用BPLED序列测量扩散时才观察到预期的衍射图案。我们展示了双极扩散梯度的校正能力，并表明当使用这种扩散梯度方案时可以获得更准确的物理参数。这些结果表明，如果将双极梯度脉冲纳入传统的扩散加权成像和DTI中，可能会得到更准确的数据。
