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目的:探讨扩散加权成像在直肠癌中的应用价值及最佳b值的选择。方法:45例直肠癌行高分辨率MRT2WI及DWI检查,DWI采用单次激发自旋回波-平面回波技术(SE-EPI),选择b值为500、800、1000、1200s/mm2,评价直肠癌的显示情况,计算肿瘤的信噪比(SNR)及肿瘤与肠周脂肪、肌肉的对比噪声比(CNR),对不同b值的图像质量进行统计分析。另20例同时行自由呼吸薄层DWI扫描,b值为1000s/mm2,行冠状面最大强度投影(MIP)及多平面重组(MPR),将图像反转及彩色化,评价其对肿瘤的显示情况。结果:在不同b值时,所有直肠癌均表现为高信号,与正常肠壁对比高于T2WI。MIP及MPR的反转图像及彩色化图像,病灶与背景产生鲜明对比,清楚直观的显示肿瘤。肿瘤的信号、SNR及肿瘤与肠周脂肪、肌肉及水的CNR随着b值的增加而下降,但与正常肠壁的对比更明显(42/45)。b=500s/mm2高信号的正常小肠显示较多,对21例直肠上段癌的判断存在一定的困难,而b≥800s/mm2正常组织结构显示少,基本不影响肿瘤的显示。b值为800s/mm2与1000s/mm2时SNR及所有CNR差异均无显著性意义,余各组间的SNR及CNR间差异均有显著性意义。结论:DWI对直肠癌显示敏感性高,b值选择800和1000s/mm2较理想。
Objective: To explore the value of diffusion weighted imaging in rectal cancer and the best choice of b value. Methods: Forty-five patients with rectal cancer underwent high-resolution MRT2WI and DWI examinations. DWI was performed by single-shot spin echo-planar echo technique (SE-EPI) with b values of 500,800,1000,1200 s / mm2 The signal intensity of tumor (SNR), the ratio of tumor to perinatal fat and muscle (CNR) were calculated. The image quality of different b values were analyzed statistically. The other 20 patients underwent free-breathing thin-film DWI with b-value of 1000s / mm2. Coronal maximum intensity projection (MIP) and multiplanar reconstruction (MPR) were performed. The images were inverted and colorized, Happening. Results: All rectal cancers showed high signal at different b values, which was higher than that of normal bowel wall compared with T2WI. Inverted images and colorized images of MIPs and MPRs contrast sharply with the background and clearly show tumors. The tumor signal, SNR and CNR of tumor, peri-intestinal fat, muscle and water decreased with the increase of b value, but more obvious compared with the normal intestinal wall (42/45). b = 500s / mm2 high signal of the normal small intestine showed more, 21 cases of rectal cancer, there are some difficulties in the judgment, and b ≥ 800s / mm2 normal tissue showed little, basically does not affect the tumor display. There was no significant difference in SNR and CNR between b values of 800s / mm2 and 1000s / mm2, with significant differences in SNR and CNR between the groups. CONCLUSIONS: DWI is highly sensitive to rectal cancer with a good b value of 800 and 1000 s / mm2.