中文摘要：

目的研究b值大小及数量对肝脏磁共振扩散加权成像（DWI）表观扩散系数（ADC）值大小及其可重复性的影响。资料与方法对39例健康志愿者行肝脏DWI扫描,使用膈肌导航单次激发平面回波序列扫描2次,分别生成b值为（0、100）、（0、500）、（0、800）、（0、100、500）和（0、100、500、800）s/mm2的ADC图像。分别在左、右肝选取3个层面,然后在每个层面各选3个圆形感兴趣区（ROI）测量ADC值,分别以左、右肝9个ROI的平均ADC值代表左、右肝的ADC值。结果 b值相同时,左肝ADC值大于右肝（P〈0.001）。b=0、100s/mm2时ADC值最大;b=0、100、500、800s/mm2时ADC值最小。Bland-Altman分析显示,b=0、100、500、800s/mm2时可重复性最好（右肝：LOA=10.5%;左肝：LOA=13.9%）。结论 b值越小,ADC值越大;使用多个b值计算的ADC值可重复性最高,在临床中测量肝脏DWI的ADC值时使用多个b值计算更为精确。

英文摘要：

Purpose To explore the effect of b value on apparent diffusion coefficient （ADC） value and its repeatability in hepatic magnetic resonance diffusion-weighted imaging （DWI）. Materials and Methods 39 healthy volunteers underwent liver DWI scan using a 1.5T magnetic resonance scanner, each of them were scanned two times of single-shot echo planar imaging sequence with diaphragm navigation technique, ADC images with b values of （0, 100） （0, 500） （0, 800） （0, 100, 500） （0, 100, 500, 800） s/mm 2 were generated respectively. Three slices of the left and the right liver were selected respectively, and three circular region of interest （ROI） on each slice were selected for the measurement of ADC values, mean ADC value of the nine ROI in the right and left liver was used to represent the left hepatic and right hepatic ADC value respectively. Results The left hepatic ADC value was greater than the right hepatic （P＆lt;0.001） when the b values were the same. The maximum ADC value was achieved when b value was 0 and 100 s/mm 2 ; the minimum ADC value was achieved when b value was 0, 100, 500 and 800 s/mm 2 . Bland-Altman analysis showed that the repeatability was best （right liver： LOA=10.5%; left liver： LOA=13.9%） when b value was 0, 100, 500 and 800 s/mm 2 . Conclusion ADC value becomes greater when b value becomes smaller; ADC value calculated from multiple b values has the best reproducibility, thus the measuring of ADC value can be more accurate by using multiple b values in hepatic DWI.