Objective:To evaluate the implications of relative apparent diffusion coefficient (rADC)derived from dif-fusion weighted imaging (DWI)in the assessment of brain metastasis and therapeutic efficacy prediction.Methods:In 21 pa-tients (a total of 42 lesions)who were pathologically or clinically diagnosed as brain metastasis,DWI and enhanced MRI scan were conducted during the follow ups (number of visits varying from 2 to 8 ),to determine the largest diameters of the tumors,as well as the ADC values for the tumor parenchyma and the white matter in normal brain,thus obtaining the re-spective rADC values.The feasibility to use rADC of the tumor parenchyma pre-treatment and the rADC value difference before and after treatment (rADC posttreatment-rADC pretreatment)for efficacy prediction was analyzed.Results:The rADCs of the tumor parenchyma pre-treatment were divided into effective group and ineffective group according to the tumor diameter changes before and after treatment,the rADCs between these 2 groups had no significant difference.2 ) The rADC value difference before and after treatment was compared to that of next treatment,the threshold to use the rADC value difference for efficacy prediction was 0.01;while the prognostic sensitivity,specificity and accuracy calculated in the present study were 92.86%,75.00%,83.33%,respectively.The consistency check showed a Kappa index of 0 .6 6 9 6 .Conclusion:The rADC value difference before and after treatment for tumor parenchyma can be used to predict the efficacy of brain metastasis treatment.A significant increase in rADC indicates the treatment is efficacious,and vice versa. Hence,rADC is believed to have certain implications in the selection of appropriate therapy regimens and the individualiza-tion of the therapy protocols.%目的：探讨磁共振扩散加权成像（DWI）相对表观扩散系数（rADC）在脑转移瘤疗效评估中的价值。方法：搜集经病理或临床确诊为脑转移瘤患者21例（共计病灶42个），随访2～8次，行DWI 及 MRI 增强扫描，测量肿瘤最大直径、肿瘤实质及对侧正常脑白质的ADC值，计算rADC值。分析肿瘤实质区治疗前rADC值或治疗前后rADC值差值（治疗后rADC值-治疗前rADC值）对疗效预测的可行性。结果：按治疗后肿瘤直径变化分为治疗有效组与无效组，两组肿瘤实质区治疗前rADC值差异无统计学意义（P＞0．05）。肿瘤实质区治疗前后rADC差值与下次治疗结果对照，rADC差值预测脑转移瘤治疗疗效的阈值为0．01，敏感度、特异度、准确度分别为92．86％、75．00％、83．33％。经一致性检验Kap-pa指数为0．6696。结论：脑转移瘤实质区rADC治疗前后差值能用于预测脑转移瘤治疗效果，rADC 值增高提示治疗有效，降低提示治疗无效，对临床治疗方式的选择和个性化治疗方案的制定有一定价值。
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