在宏观静止中感受微观运动:磁共振扩散加权成像临床应用的若干认识

Exploring micro-motion in macro-stillness:some insights about clinical application of diffusion-weighted MR imaging

DWI利用磁共振特殊序列突出了扩散引起的散相位作用,在宏观成像中反映活体组织中水分子的微观扩散运动,有必要将病变的扩散特征作为重要的影像学特征来加以认识.采用ASSET-EPI技术使DWI的空间分辨率和图像质量得到提高;通过增加信号平均次数,可基本消除EPI伪影及ASSET相关伪影;应用分次屏气采集的方法可获得较为满意的腹部DWI图像.高b值(800～1000 s/mm2)的DWI已经在乳腺、胃、肝脏、直肠、子宫、前列腺等领域的临床应用获得成功,显示出良好的应用前景.临床研究结果表明,DWI对可在一定程度上显示未出现明显形态学改变的病变区域;表观弥散系数(ADC)值作为量化指标可为肉眼不易区分的病变提准确判断;以病变区的相对值作为定量指标,在反映病变组织特征方面具有一定的临床应用价值;DWI联合其他MRI技术,有助于客观评价DWI的临床价值,并可在更深层次上拓展对疾病的认识.

Diffusion-weighted imaging （DWI）, by adopting a special sequence to give prominence to scattered phases caused by water diffusion, allows in vivo demonstration of micro-diffusion process in macro-imaging. It is necessary to take diffusion trait of lesion as an important imaging character to study. ASSET-EPI technique improve the quality of spatial resolution and image quality of diffusion weighted image; increasing numbers of excitation approximately eliminate EPI and ASSET related artifacts; separated breath hold acquisition technique helps to acquire better diffusion images of abdomen. Clinical applications of DWI at a high b values （800--1000 s/mm^2） had gained success in many fields, such as breast, stomach, liver, rectum, uterus and prostate and so on, which showed a promising prospect. Clinical research had showed that, signal changes in DWI could, to certain extent, reveal abnormality with yet no morphologically distortion; and apparent diffusion coefficient （ADC） value, a quantitative index, may provide a rather accurate evaluation for undetectable loci by naked eyes. Besides, relative index such as ratio of ADC value of lesion to surrounding tissue, also showed value in reflect specific histo- logical characteristic of lesion in clinical application. Combined applications of DWI with other imaging techniques will be helpful to evaluate its clinical value objectively and fully understand the disease in a profound inspection.