Diffusion Weighted Imaging And Pathologic Correlation Of Rabbit VX2Soft-tissue Tumor

Section I Establishment of VX2Soft-tissue Tumor Model and Magnetic Resonance Weighted Imaging Study in RabbitsObjective:To establish an experimental animal model of soft-tissue tumor, observe the growth characteristics and investigate the applicative value of magnetic resonance weighted imaging in them.Methods:10New Zealand white rabbits were implanted with0.03ml VX2tumor tissue suspension in the left and right proximal thighs.9days、14days and21days later, MR plain scan, weighted scan and strengthen MR were performed on these rabbits respectively, observing the growth of tumors, comparing the differences of signal intensity of tumors tissue, muscle tissue, the background and signal ratio (SNR), contrast noise ratio (CNR)and the diffusion coefficient of the apparent (ADC) ratio of tumor tissue, muscle tissue in the different b values(200、500、1000s/mm2) in14days.Results:Rate of tumor formation was100%. Without subcutaneous implant. The tumors were round or oval.9days; there were no necrosis of tumors. T1WI was similar to or slightly low signal, T2WI showed homogeneous high signal, and the enhanced was homogeneously. Average length diameter was1.634±0.304cm.14days, there were multifocal necrosis in the tumors, T1WI was slightly lower or low signal, T2WI showed slightly higher or high signal, and the occurrence of edema surrounding with long T1,T2signals. Multiple point like no strengthening area with enhanced MRI. Average length diameter was2.622±0.141cm;21days, there were obvious liquefaction, necrosis in the tumors. Uneven low intensity signal based on T1WI, T2WI showed uneven high intensity signal, and enhanced mostly ring enhancement, internal common short T1and long T2signal after bleeding, no enhancement. Average length diameter was4.290±0.243cm The ADC values and signal intensity of the different parts was gradually declined with increases of b value. The average ADC values of tumor tissue were1.257±0.098,1.163±0.088,1.061±0.054and significant difference.b value of1000s/mm2,the measured ADC value ranges were smaller, indicating more stable and accurate.Conclusion:In the observation of tumor growth, there were rare necrosis and biological characteristics relative stability in VX2rabbit soft tissue tumor from9d to14d, and more suitable for imagingstudies.When b=1000s/mm2,although the quality of DWI imaging were decline and part of the visible deformation to some degrees, but it better reflects the diffusion information of water molecular within the tumor tissue, and improves the contrast to the surrounding tissue, also the measurement of ADC values more accurate. b=1000s/mm2can be used as a suitable value of DWI imaging in the rabbit VX2portability soft-tissue tumor model.Section Ⅱ Evaluation of Cell Proliferation of Rabbit VX2Portability Soft-tissue Tumor Cells by Diffusion Weighted ImagingObjective:To evaluate the relationship between ADC values generated from MR diffusion weighted imaging (DWI) and cell density, the PCNA labeling indices which reflect the cell proliferation of VX2tumor in the soft-tissue of rabbit.Methods:VX2tumor tissue suspension was inoculated in the muscular tissue of the left and right proximal thighs of10healthy New Zealand white rabbits, on which DWI was performed2weeks later. Apparent diffusion coefficient (ADC) maps were generated from DWI images using the software on MR scanner. ADC values were measured in3regions of interest (ROIs) for the solid part of each tumor. The rabbits were sacrificed after MR imaging. The gross specimens of tumors were obtained and tumor tissues were taken from the non-necrotic regions corresponding to ROIs on DWI images. For HE dyeing and calculate cell density.At the same time PCNA immunostaining of obtained tumor tissues was performed to measure their PCNA labeling indices. The correlation between ADC values and cell density, PCNA labeling indices was evaluated by Pearson correlative analysis.Results:All of the tumor in the rabbit VX2growing success. Without subcutaneous implant. Tumor growth in good condition, size20-30mm. Totally20pieces of VX2tumor tissues were analyzed. The average of ADC value of tumor solid part was1.067±0.154×10-3mm2/s; the average of cell density was40.8%±7.8%;the average of PCNA labeling index was60.2%±15.5%There was a significant negative correlation between their cell density,PCNAlabeling indices and ADC values, r=-0.806, P<0.001and r=-0.734, P<0.001.Conclusion:There was a significant negative correlation between ADC values and their cell density, PCNA labeling indices. ADC value may be used in evaluating the cell proliferation of soft-tissue tumor through its reflection of cell density and PCNA labeling index, and therefore is helpful in evaluating the prognosis of soft-tissue tumor, making plan for their treatment and monitoring the effect of their therapies.