3.0 T MR扩散加权成像评价兔肝VX2瘤射频消融治疗的实验研究

目的 探讨3.0 T MR DWI评价兔肝VX2瘤射频消融治疗疗效的价值.方法 新西兰大白兔22只.20只用于建立VX2瘤模型,2只健康正常兔用于行正常肝射频消融术对照.于VX2瘤种植后14～21 d(平均17 d),对符合实验条件瘤兔(病灶位于肝实质内,最大直径≤3 cm,坏死病灶直径≤整个病灶直径的1/2)行3.0 T常规MRI和功能DWI.对瘤兔及对照组正常兔行射频消融治疗,射频消融术后7～10 d(平均8 d)行3.0 T常规MRI及DWI.所有射频消融治疗兔行MR检查后均行病理检查.测量兔肝VX2瘤、正常兔肝射频消融治疗前后ADC值,分析兔肝VX2瘤射频消融治疗前后3.0 T MR常规成像、ADC值特征,并与病理对照.同一b值射频消融治疗后不同组织间ADC值比较采用重复测量资料方差分析.结果 20只实验组兔肝VX2瘤模型均建立成功,1例肿瘤突出于肝表面、1例肿瘤病灶出现明显坏死未纳入实验.所有18个瘤灶及2例正常兔肝射频消融均成功.兔VX2瘤T1WI序列表现为低或等信号,T2WI为高信号.肝VX2瘤兔射频消融治疗后7～10 d,射频消融病灶T1WI序列表现为低或稍高信号,T2WI为混杂信号.T2WI序列周边环形稍高信号为肉芽组织,增强扫描明显强化,T2WI序列低、中等信号为凝固性坏死.坏死组织在DWI图上为低信号,活性肿瘤组织位于病灶周边,呈结节状,在T2WI、DWI图上为等或稍高信号.肿瘤标本为灰白色,部分肿瘤组织间夹杂增生血管、少许肉芽组织.b值为600 s/mm2时,射频消融治疗后活性肿瘤组织(9只)、坏死组织(18只)、肉芽组织(18只)、正常组织(18只)ADC值分别为:(1.227±0.140)×10-3、(0.702±0.050)×10-3、(1.918±0.124)×10-3、(1.739±0.044)×10-3mm2/s,各组间ADC值差异具有统计学意义(P＜0.01).b值分别为200、400、600、800、1000 s/mm2时治疗后坏死组织、活性残留或复发肿瘤组织、肉芽组织、正常肝组织间ADC值差异具有统计学意义(P＜0.01).结论 兔VX2瘤模型适合3.0 T MR评价射频消融治疗疗效的动物实验研究,对射频消融治疗基础及临床应用研究具有重要价值.

3.0 T MR diffusion weighted imaging in the evaluation of radio-frequency ablation of the liver VX2 tumors

Objective To evaluate 3.0 T MR DWI techniques in detecting the lesions of pre and post-radiofrequency ablation of the rabbit liver VX2 tumors. Methods Twenty two New Zealand white rabbits were used in this experiment. Twenty tumor fragments were implanted into the livers of 20 rabbits respectively. Two normal rabbits were used as controls for radiofrequency ablation of the normal liver. 3.0 T MR DWI was performed 14 to 21 days after tumor implantation (mean, 17 days) in the tumor-bearing animals. Radiofrequency ablation was performed in the 18 tumor-bearing animals and in the two healthy animals. 3.0 T MRI and DWI were performed 7 to 10 days after radiofrequency ablation (mean, 8 days).Pathology was obtained immediately after the completion of post-radiofrequency ablation MR imaging. The MRI features and ADC values of pre- and post -radiofrequency ablation lesions in the liyers with VX2 tumors and normal rabbits were analyzed and correlation was made with histopathologic findings. Analysis of variance repeated measures were performed in analyzing the differences among the ADC values of different tissues with the same b value. Results All 20 rabbit liver models of VX2 tumors were constructed successfully. One rabbit died of anesthetic overdose, another one showed necrosis within the implanted tumor. All 18 untreated VX2 tumors had predominantly low or iso-signal intensity on T1 WI and high signal intensity on T2WI. All 18 VX2 tumors and 2 normal rabbits were treated by radiofrequency ablation successfully. Lesions treated by Radiofrequency ablation displayed low signal intensity on T1 WI, and high signal intensity on T2WI. Seven to 10 days after radiofrequency ablation, lesions varied from having low signal intensity to slightly increased signal intensity on T1 WI, with areas of mixed ( high, intermediate, and low) signal intensity. A peripheral rim of high signal intensity with varying thickness on T2WI correlated with granulation tissue, which exhibited intense enhancement on contrast-enhanced images. Areas of low to intermediate signal intensity within the lesion on T2WI corresponded to coagulation necrosis. The tumor tissue appeared as areas of peripheral nedularity, with intermediate to high signal intensity on T2-weighted images and DWI. The tumor specimen was gray, among the tumor tissue, there were hyperplastic vessels,and granulation tissue. When b value was 600 s/mm2 , the ADC value of viable tumor (9 cases), necrosis (18 cases), granulation tissue ( 18 cases), normal liver tissue ( 18 cases) were ( 1. 227 ±0. 140) × 10-3,(0. 702 ± 0. 050)×10-3, ( 1.918 ± 0.124) × 10-3, ( 1. 739 ± 0. 044 ) × 10-3 mm2/s, respectively, which were statistically significant (P ＜0. 01 ). When b =200,400,600,800,1000 s/mm2, the differences of ADC values among viable tumor, granulation tissue, necrosis,normal liver tissue were also statistically significant ( P ＜0. 01 ). Conclusion The rabbit liver VX2 tumor models and 3.0 T MR DWI are important tools in the basic and clinical researches of radiofrequency ablation.