Experimental Study On The Feasibility Of Functional MR Imaging In Qualitative Lymph Nodes And Evaluating The Response Of Lymph Nodes To Radiotherapy

Part 1 Evaluation of benign from malignant lymph nodes using diffusion weighted imaging in rabbit modelsObjective:To explore the value of diffusion weighted imaging(DWI)in differentiating benign and malignant lymph nodes.Methods:Thirty-two healthy New Zealand rabbits were randomly divided into benign and malignant groups(16 rabbits per group).The benign(16 lymph nodes)and metastatic lymph node model(malignant group,a total of 16 lymph nodes)were established,respectively.All rabbits underwent the MRI examination.The apparent diffusion coefficients of lymph node(ADClymph node)and of ipsilateral muscle at the same plane(ADCmusele)were measured.Relative ADC(rADC)were obtained as following:rADC＝ADClymph node/ADCmuscle.The ADC and rADC values of benign and malignant lymph nodes were compared by using independent sample t test,and the efficacy of ADC and rADC in qualitative diagnosis of lymph nodes was analyzed by ROC curve.Results:Both benign and malignant lymph nodes showed the relatively high signal on DWI.The ADC and rADC values between the benign and malignant lymph nodes were statistically significant[(0.92±0.13)×10-3 mm2/s vs(0.76±0.08)×10-3 mm2/s;0.71±0.05 vs 0.63±0.05,respectively,and all P<0.05].When ADC and rADC are used to differentiate benign and malignant nodes,the area under the receiver operating characteristic curve was 0.82 for ADC(the threshold of 0.84× 10-3 mm2/s)and 0.88 for rADC(the threshold of 0.66),and no significant difference was found between the two methods(P>0.05).Conclusion:DWI enables the differentiation of benign from malignant lymph nodes.And rADC did not improve the capacity of ADC for differentiating of benign from malignant lymph nodes.Part 2 Feasibility study of BOLD MRI in evaluating the response of metastatic lymph nodes of rabbit VX2 tumor to radiotherapyheObjective:To investigate the feasibility of blood oxygen level-dependent MRI in evaluating the response of metastatic lymph nodes of rabbit VX2 tumor to radiotherapy.Methods:Twenty-eight healthy New Zealand white rabbits,male or female,2 to 3 months,weighing 2 to 3 kg,were used to establish the animal model of VX2 tumor popliteal fossa metastatic lymph node,and then were divided into either the radiotherapy group(n=16)or the control group(n=12).The radiotherapy group received a 20Gy radiotherapy per rabbit,the control group received sham radiotherapy.All rabbits underwent MRI scan on four time points,including before(0 day),3rd,7th and 14th days after radiotherapy.The two parameters of size and R2*value(s-1)of lymph node were measured.At each time point,two rabbits in each group were sacrificed randomly to resect lymph nodes for pathological examination,and two parameters of microvessel density(MVD,strip/HP)and apoptosis index(AI,%)were analyzed.The parameters among the four time points in each group or between the two groups were compared.The correlation of lymph node size and R2*value with MVD or AI was analyzed,respectively.Results:A significant size difference was neither between the two groups or among the time points in each group(P>0.05).The R2*of lymph node in the radiotherapy group was 29.56±1.66,36.78±2.56,44.79±5.80,57.74±6.23 at the time points of 0,3,7 and 14 days,respectively,showing a gradual increase trend;MVD was 52.33±2.52,41.00±3.61,34.00±3.61 and 22.67±2.52,respectively,showing a decreasing trend;AI was 12.75±0.50,14.86±0.58,20.60±0.46 and 27.53±0.71,respectively,showing a gradual increase trend(all P<0.05).In the control group,both R2*value and AI among the four time points did not change statistically(all P>0.05),which were 29.44±2.36,29.65±1.81,30.11±1.31and 30.86±1.11;13.10±0.30,13.73±0.70,13.97±1.25 and 13,63±0.75,respectively.But MVD shown a gradual increase trend(50.00±3.00,53.00±1.73,60.33±2.52 and 70.00±2.00,respectively,P<0.05).There were significant differences in R2*and MVD at 3,7 and 14 days,in AI at 7 and 14 days between the two groups(all P<0.05).There was a linear correlation of R2*value,but not of size,with MVD and AI(r=-0.87 and 0.94,respectively).Conclusion:BOLD MRI indirectly reflected the hypoxic status of metastatic lymph nodes after radiotherapy,and has potential value in evaluating the response of metastatic lymph nodes to radiotherapy.