兔肢体VX2软组织肿瘤MR扩散加权成像

目的:建立兔肢体软组织肿瘤模型,探讨MR扩散加权成像在软组织肿瘤诊断中应用的可行性及适用于软组织肿瘤成像的合适的b值。方法:25只新西兰大白兔(月龄2～3个月,体重1.5～2.0kg,雌雄不限),将肿瘤瘤株种植在左前上肢内侧。在种植瘤株后2～3周使用1.5T磁共振仪行常规MRI及DWI检查,b值取200、400、600、800和1000s/mm2。在MRI检查后3～4周分批处死荷瘤兔,取出肿瘤组织,观察肿瘤的大体形态及病理学表现。结果:肿瘤成瘤率96%(24/25)。种瘤后14、21和28天,肿瘤直径分别约为2.0、4.0和5.5cm。肿瘤直径比较小(14天)时,质地硬,肿瘤坏死、瘤周水肿很少见。在常规T1WI上肿瘤实质多呈等信号,瘤内出血少见;T2WI上肿瘤实质为不均匀高信号,肿瘤中央和瘤周可见信号更高的坏死、水肿区;增强后肿瘤实质明显强化,肿瘤边缘强化更显著。DWI图像上,当b值较小时(200s/mm2)受T2透过效应影响明显,b值比较大时(1000s/mm2)图像信噪比下降明显,b值为600和800s/mm2时,图像质量比较好;b值为200、400、600、800和1000s/mm2时肿瘤的ADC值分别为(1.56±0.11)、(1.32±0.12)、(1.25±0.10)、(1.19±0.08)和(1.14±0.07)mm2/s;b值为600和800s/mm2时,肿瘤实质的ADC值明显小于坏死区及周围肌肉组织,差异有显著性意义(P<0.005)。结论:DWI可以用于兔肢体VX2软组织肿瘤的观察,b值为600和800s/mm2时可以获得比较好的DWI图像。肿瘤组织、肌肉组织及坏死组织的ADC值明显不同,DWI在软组织肿瘤的诊断和预后评估等方面具有广阔的应用前景。

Diffusion-weighted MR imaging in rabbit extremity VX2 soft tissue tumor

Objective：To establish VX2 soft-tissue tumor model in rabbit extremity,evaluate the feasibility of the application of DWI and select the optimal b value.Methods：25 New-Zealand white rabbits（2~3 months old,weight 1.5~2.0kg） were implanted VX2 tumor in the inner side of forelimb.All rabbits underwent conventional MR and DWI examination 2~3 weeks after implantation of tumor with a 1.5T MR scanner,with b values of 200、400、600、800 and 1000s/mm2 respectively.All the rabbits were sacrificed in batches after the implantation of tumors,tumors morphology and pathology data were analyzed.Results：24 of all 25 rabbits（96%） were successfully implanted VX2 tumor.The diameter of tumors reached 2.0,4.0 and 5.5cm at the 14,21 and 28 days.Tumors were hard,necrosis and peritumoral edema were rare at the second week after implantation,which showed high signal intensity on T2WI.The parenchyma of tumor showed iso-intensity on T1WI and heterogeneously hyper-intensity on T2WI respectively in comparison with the muscle,and manifested apparent enhancement after the injection of Gd-DTPA.The enhancement of tumor rim was even more conspicuous.DWI was affected by T2 shine through effect at low b value（200s/mm2）.Signal-to-noise would decrease with large b value（1000s/mm2）.ADC values were（1.56±0.11）,（1.32±0.12）,（1.25±0.10）,（1.19±0.08） and（1.14±0.07）mm2/s,while the b values were 200,400,600,800 and 1000s/mm2 respectively.Along with the increasing of b value,the value of ADC decreased.We deemed that DWI would be better with b value at 600 and 800s/mm2.There were significant differences of ADC values between tumor parenchyma,necrosis and muscle tissue,and the ADC value of tumor parenchyma was smaller than necrosis and muscle tissue.Conclusion：The application of DWI in the rabbit extremity VX2 sarcoma is feasible.ADC values were different among tumor parenchyma,normal muscle and necrosis.DWI could provide valuable information for differential diagnosis and monitoring the prognosis of STT,aid in the distinction between necrotic and viable tumor,and also be useful in the differentiation between post-therapeutic changes and tumor recurrences.