Evaluation of MR lymphography with positive lymphotropic contrast agent in diagnosing lymph node lesions

Abstract

Objective To evaluate the interstital MR lymphography using positive lymphotropic contrast agent for differentiation of metastatic lymph nodes from inflammatory lymph nodes hyperplasm.Methods Eighteen New Zealand white rabbits weighted at 2.0-2.5 kg were used.Inflammatory hyperplastic popliteal lymph node model was established in 9 rabbits by injection of complete freund adjuvant into the interdigitial skin of the dorsal aspect of one hind leg,and tumor-bearing popliteal lymph node model was established in another 9 rabbits by injection of VX~2 tumor cell suspension.The popliteal lymph nodes of another hind leg of all 18 rabbits were assigned to the normal contral group.In each group,every rabbit underwent MR lymphography examination before and after the inoculation.Volumes of 0.2 ml of Gd[DTPA-bis(2-aminoethoxy)ethane]polymeric contrast agent(Gd-poly-DTPA-EOEA)injection were injected subcutaneously into the dorsal feet of both hind legs of two groups of rabbits.T_1-weighted 3D gradient-echo images were obtained,and source images were used to reconstruct images of MIP before and after the administration of agent.The maximum short-axis diameter(MSAD)of each popliteal lymph node was measured on the enhanced 3D MIP images,and the signal-to-noise ratio(SNR)measurement was performed in the largest popliteal node of each rabbit at each time point in delayed scan.Independentsamples t test was used to compare the sizes of popliteal nodes in MSADs between inflammatorily hyperplastic and tumor-bearing nodes after the inoculation,and the values of SNRs of popliteal nodes at each time point between inflammatorily hyperplastic,tumor-bearing and normal popliteal lymph nodes.Imaging results of the popliteal nodes were analyzed and correlated with pathological findings.Results All of the rabbits were successfully inoculated except of the 2 rabbits in tumor-bearing nodal group.The size in MSAD of 13 inflammatorily hyperplastic and 11 tumor-bearing nodes was(1.32±0.14)and(1.33±0.12)cm,respectively.There was no significant statistical difference between the sizes of the two groups(t=0.186,P＞0.05).At the time of 5,15,30,60,90,120 minutes after the injection of the agent,the value of SNR of 9 inflammatorily hyperplastic and 9 contralateral normal nodes was 17.31±0.37 and 17.19±0.29,27.42±0.50 and 27.39±0.48,38.44±0.47 and 38.19±0.27,37.10±0.09 and 36.97±0.10,36.32±0.61 and 36.20±0.80,34.60±0.44 and 34.71±0.32,respectively.There was no significant statistical difference between the values of the two groups(t=0.78,0.14,1.43,1.00,0.36,-0.62,respectively,P＞0.05).The value of SNR of seven tumor-bearing and seven contralateral normal nodes was 6.00±0.22 and 17.21±0.28,7.87±0.16 and 27.17±0.23,8.14±0.24 and 38.16±0.19,8.09±0.28 and 36.94±0.30,7.59±0.20 and 35.96±0.72,7.50±0.14 and 34.81±0.27,respectively.There was significant statistical difference between the values of the two groups(t=-84.00,-182.72,-261.27,-186.48,-100.22,-239.00,respectively,P＜0.01).At each time point,inflammatorily hyperplastic nodes had significantly higher values of SNRs compared to tumor-bearing nodes(t=83.97,174.07,158.49,152.71,96.06,154.57,respectively,P＜0.01).A complete or part signal filling defect occurred in the tumor-bearing lymph node on the MR lymphographic images.Conclusions The internal anatomy and function of the lymph nodes were effectively visualized by interstitial MR lymphography with positive lymphotropic contrast agent,which provide a sensitively diagnostic way for the differentiation of benign lymph nodes from malignant ones. Key words: Lymphography; Contrast media; Magnetic resonance imaging; Neoplasm metastasis; Inflammation