目的 比较两种高b值磁共振 弥散加权成像 ( d i f f u s i o n w e i g h t e d imaging，DWI)在直肠病变诊断中的应用 价值。方法 使用3.0T MRI对直肠癌进行 常规直肠扫描及DWI扫描，DWl采用平面回 波(echo planar imaging，EPI)序列， 选用2个不同的b值(1000s/mm2 、2500s/ m m2 )，测量肿瘤及同侧臀大肌在不同b 值下DWI图像上表观弥散系数(apparent diffusion coefficient，ADC)，并进行 比较分析。结果 b值等于1000s/mm2 时， 肿瘤的ADC值为(0.923±0.15)×10-3mm2 / s，而臀大肌的ADC值为1.57±0.091×10- 3 mm2 /s，b值等于2500s/mm2 时，肿瘤的ADC 值为(0.642±0.07)×10-3mm2 /s，而臀大 肌的ADC值为(0.925±0.12)×10-3mm2 /s。 所得肿瘤与臀大肌的ADC比值两组间存在 差异。结论 b值等于1000s/mm2 组的DWI图 像的ADC比值高于2500s/mm2 组，更加有利 于显示病变，ADC值可作为直肠癌诊断及 评价预后的指标之一。

Objective To compare the appicaiton value btween the two different high b value of diffusion weighted imaging (DWI) in colorectal carcinoma. Methods All patients with rectal carcinoma underwent conventional scanning and DWI scanning by 3.0T MRI. In DWI, two different b value (1000 and 2500s/mm2 )were used. The ADC value of tumor and ipsilateral gluteus maximus under different b value on DWI were measured and compared. Results When b value is 1000s/mm2 , ADC value in tumor was (0.923±0.15)×10-3mm2 /s, and in glutes were (1.57±0.091)×10-3mm2 , when b value is 2500s/mm2, ADC value in tumor was (0.642±0.07)×10-3mm2 /s, and in glutes were (0.925±0.12)×10-3mm2 /s. There was significant difference in ADC ratio of tumor and glutes between the two groups. Conclusion The value of ADC ratio in the group which b value is 1000 s/mm2 was higher than that whose b value is 2500s/mm2 , ADC value can be used as a index of diagnosis and prognosis evaluation for rectal cancer.