Comparison Between DWI And Gd-DTPA-enhanced MRI In Diagnosing Metastatic Lymph Nodes Of Head And Neck In Rabbit Modes

[Objective]:To establish animal modes of benign and malignant lymph nodes with New Zealand white rabbits. To compare the diagnostic accuracy of the relative apparent diffusion coefficient(rADC) with gadolinium-enhanced MR in differentiating the metastatic lymph nodes in head and neck rabbit models,by using histologic analysis as the reference standard.[Materials and Methods]:20New Zealand white rabbits,male or female, age3to4months, body weight2.0-2.5kg, were randomly divided into two groups with10rabbits in each group.Established model of inflammation group:Making blend of egg yolk emulsion with raw egg yolk and saline1:1volume.The emulsion was inoculated concentrically between the lateral auricle edge and the central auricular artery into the cranial section of the lower third of right auricles by injecting3ml of blend of egg yolk emulsion.The same procedure was repeated after three days.From the first day after inoculation,growth and the head and neck lymph node enlargement were observed every day.Established model of VX2carcinoma malignant group:Cut the Vigorous growth strong fish-like organization of tumor edge in VX2tumor-bearing rabbit, made into tumor cell suspension of1×10ml;10rabbits Were anesthetized with3%sodium pentobarbital (30mg/kg) via marginal ear vein,VX2carcinoma was inoculated concentrically between the lateral auricle edge and the central auricular artery into the cranial section of the lower third of right auricles by injecting tumor cell suspension0.5ml.Intramuscular injection (4×105U/day) of penicilin was administered for the three consecutive days to prevent infection. From the first day after inoculation,growth and the head and neck lymph node enlargement were observed every day.All subjects were examined with GE1.5T signal HDT MR scanner using knee coil. Rabbits were anesthetized with3%sodium pentobarbital (30mg/kg) via the marginal ear vein Straighten rabbits neck, Supine position, feet first. Scan range was from the ears roots connect to the thoracic inlet.Scanning sequences included cross sectional FSE T1-weighted image(TlWI), cross sectional FSE T2-weighted image(T2WI),and cross sectional diffusion weighted imaging (DWI) sequence scan were performed on each model, After80seconds administration of Gd-DTPA FSE T1WI were acquired. lymph nodes, the same level of muscle’s ADC values were measured and lymph node/muscle rADC value were calculated.lymph nodes/the same level of muscle’s standardized signal intensities (SI) values were measured before and after Gd-DTPA enhanced T1WI sequences, the SIpost/SIpre value (SIr)were calculate and analyzed statistically. Finally get the lymph nodes, measuring the size of lymph nodes, and diagnose the nature of lymph node by histopathology HE staining.[Results]:Confirmed by pathology, the number of lymph nodes from inflammation group were26, the number of lymph nodes from tumor group were14. The long diameter of metastasis lymph node is12.29±3.80mm, short diameter is7.95±2.10mm;the long diameter of inflammatory lymph nodes is9.40±1.90mm, short diameter is5.60±2.10mm. The number of the metastasis lymph nodes short diameter<10mm is9, the number of long diameter/short diameter≥2is3; inflammatory lymph nodes2short diameter>10mm, the number of long diameter/short diameter≤2is15,3lymph nodes has central necrosis.The rADC value of inflammation group lymph nods is1.05±0.09, the rADC value of malignant group lymph nods is0.78±0.10;the SIr value of inflammation group lymph nods is1.34±0.25, the SIr value of malignant group lymph nods is1.78±0.33.Independent-Samples T Test were conducted to compare the differences of benign and malignant lymph nodes.rADC value, Sir value,both were statistically significant (t value were-8.30、4.76respectively,all P <0.05).A receiver operating characteristic analysis was conducted to compare the diagnostic value of rADC value and SIr value,when using rADC value area under the ROC curve (AUC) was0.93, and the threshold value of rADC was0.88, while the sensitivity, specificity was92.3%,92.9%respectively; when using SIr value the AUC area was0.81, the threshold was1.66, the sensitivity, specificity was78.6%,88.5%respectively.[Conclusion]:The diameter of malignant lymph node and inflammatory lymph node, long diameter/short diameter values overlap larger. There is a difference of rADC value and SIr value of lymph nodes between Inflammation and neoplasms metastasis groups. rADC value can be more accurate than SIr value in differentiating benign and malignant lymph nodes in rabbit models.