磁共振弥散成像中T2穿透效应的影响及解决方法研究

Investigation and Solution for T2 Shine-Through Effects in MR Diffusion-Weighted Imaging

目的:探讨磁共振弥散成像中的T2穿透效应,及从根本上消除该效应的方法。方法:应用1.5T超导MR系统及自旋平面回波成像序列,对30名志愿者采集含脑干部位的头部弥散成像数据;除通常采集的b≠0及对应TE的b=0的数据外,额外采集一组更短TE的b=0数据,从两组不同TE的b=0数据,计算像素组织的T2值,并用它除去b≠0图像数据中的T2衰减,得到无T2穿透效应的弥散加权图像数据。结果:脑干小脑上脚交叉结构较之周边组织有较长的T2值。在消除了T2穿透效应后,正常脑干区小脑上脚交叉部分和脑干区皮质脊髓束部分在弥散加权图像上的信号差异消失。结论:通过采集两组不同TE的b=0数据,计算得到每个像素组织的T2值;应用得到的T2值从b≠0的弥散加权图像中去除T2衰减,可以完全去除弥散成像中的T2穿透效应。

Purpose： To investigate the effect and find solution to completely remove T2 shine-through in diffusion-weighted MR imaging. Methods： Using 1.5T MRI system and echo-planar diffusion-weighted imaging sequence, 30 volunteers were imaged and head data encompassing the brain stem anatomy were collected. In addition to the regular data of b≠0 and b=0 at same TE, an additional data of b=0 with much shorter TE was also collected. From the two b=0 data, tissue T2 value were determined pixel by pixel and were used to remove the T2-decay from the b≠0 data, thus completely removing the T2 shine-through from the diffusion-weighted MR image data. Results： The decussation of superior cerebellar peduncle in human brain stem has higher T2 values than its surrounding tissues. After removing of the T2 shine-through effects, the signal difference between the decussation of superior cerebellar peduncle and the corticospinal tracts in human brain stem in diffusion-weighted MR images was also eliminated. Conclusions： By acquiring b=0 images with two different TE values, tissue T2 value is determined pixel by pixel. Using the T2 value, T2-decay is removed from the b≠0 data, thus completely eliminating the T2 shine-through effect in diffusion-weighted MR imaging.