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

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.

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

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/mm2) 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 foci by naked eyes. Besides, relative index such as ratio of ADC value of lesion to surrounding tissue, also showed value in reflect specific histological 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.