Evaluation Intramedullary Invasion Of Malignant Bone Tumor By DCE-MRI Quantitative Parameters In Animal Study

Objective To analyze the difference of quantitative parameters in tumor solid area,micro-invasive area and area without tumor cells（pure edema area and adjacent bone marrow area）of VX2 malignant bone tumor in rabbits by DCE-MRI,and to explore the value of DCE-MRI quantitative parameters in evaluating micro-invasive areas of malignant bone tumors.Methods Sixty purebred New Zealand white rabbits were used to establish VX2malignant bone tumor models in the proximal metaphysis of the right tibia.The models were examined by conventional MRI and DCE-MRI three weeks ago,then they were executed.Right tibia of the models were taken for gross specimens and pathological sections.Distal margin of the intramedullary tumors were observed in pathological sections,then the margin areas of the tumors were divided into microscopic infiltration group and non-microscopic infiltration group.For the group with micro-infiltration,the range of infiltration area was determined in pathological section,and corresponding DCE images were analyzed quantitatively by extended tofes linear model,quantitative parameters of tumor margin parenchyma areas,micro-infiltration areas and non-tumor cell areas were obtained.The corresponding parameters of the marginal parenchyma areas and non-tumor cell areas were measured in the group without micro-infiltration.Quantitative parameters include volume transfer coefficient（Ktrans）,rate constant（kep）,extravascular extracellular space volume（Ve）,and volume fraction of intravascular contrast agent（Vp）.One-way ANOVA was used to compare the differences between the parameters of the three areas.Two independent sample t test were used to analysis the differences among the parameters in the two areas in non-microscopic infiltration group.The Receiver Operating Characteristic Curves（ROCs）were plotted,and the accuracy of distinguishing different regions by different parameters were calculated according to the area under curve（AUC）.SPSS19.0 software were used for statistical processing.Results（1）Fifty-eight models were successfully prepared with a success rate of 96.7%.A total of 39 models were selected for the final test.Among them,22 cases（22/39,56.4%）were divided into the micro-infiltration group,17 cases（17/39,43.6%）were divided into the non-micro-infiltration group.The infiltration depth in the micro-infiltration group ranged from 1.3 mm to 4.6 mm,with an average infiltration depth of 3.2 mm±0.8 mm.（2）The statistical results of quantitative parameters in different areas of micro-infiltration group were as follows:Ktrans values were（0.494±0.052）,（0.403±0.049）,（0.173±0.047）min-1（p=0.000）,Kep values were（1.959±0.65）,（1.528±0.372）,（1.174±0.486）min-1（p=0.000）,Ve values were（0.247±0.068）,（0.283±0.057）,（0.168±0.062）min^-1（p=0.000）,Vp values were（0.125±0.036）,（0.108±0.033）,（0.098±0.025）min^-1（p=0.022）,respectively.There were significant difference in quantitative parameters among the three regions.There were no significant difference in Vp values between the tumor margin parenchyma areas and micro-infiltration areas（p=0.078）,micro-infiltration area and the bone marrow area（p=0.315）,and Ve values between the tumor margin parenchyma areas and micro-infiltration areas（p=0.056）after comparing between groups.（3）The Ktrans value,Kep value,Kep value,Ve value of the non-infiltration group were as follows:（0.549±0.078）and（0.171±0.043）（p=0.000）,（1.800±0.572）and（1.343±0.353）（p=0.006）,（0.284±0.073）and（0.173±0.062）（p=0.000）.The difference was statistically significant（p<0.05）.（4）Ktrans had highest accuracy in differentiating solid area from micro-infiltration area（AUC=0.990）,micro-infiltration area from non-tumor cell area（ACU=0.992）,and solid area from non-tumor cell area（AUC=1.000）,respectively.The accurary of Ve was higher in differentiating micro-infiltration area from non-tumor cell area（AUC=0.915）.Kep had certain accurary in differentiating solid area from micro-infiltration area（AUC=0.702）,micro-infiltration area from non-tumor cell area（AUC=0.713）,and solid area from non-tumor cell area（AUC=0.712）,respectively.Ve and Vp had certain accuracy in differentiating solid area from non-tumor cell area,AUC were 0.884 and0.731,respectively.Ve had lower accuracy in differentiating solid area from micro-infiltration area（AUC<0.7）.Vp had lower accuracy in differentiating solid area from micro-infiltration area and micro-infiltration area from non-tumor cell area（AUC<0.7）.Conclusion:Quantitative parameters Ktrans,kep can effectively distinguish solid areas of the tumor,micro-infiltration areas and non-tumor cell areas,and Ktrans have the highest accurary.Ve can be used to distinguish areas with and without tumor cells.Vp can distinguish solid areas of the tumor form non-tumor cell areas.Quantitative parameters of DCE-MRI can assess the extent of intramedullary infiltration of malignant bone tumors.