Tracking Transplanted Pancreatic Islet Cells In Rats Using 3.0T MRI

PartⅠStudy of labeling pancreatic islet cells with superparamagnetic iron oxide (SPIO) and tracking labeled cells using MRI in vitroObjective:To label pancreatic islet cells with superparamagnetic iron oxide(SPIO) and track labeled ceils using MRI in vitro.Methods:Pancreatic islet cells were isolated from Wistar rats and Lewis rats,and then labeled with SPIO combined with PLL by means of receptor-mediated endocytosis.20-30 handpicked pancreatic islet cells were put in the Ependoff tube for a standard T2~*-weighted gradient echo sequence scanning on a GE 3.0T Signa Excite MR scanner equipped with an animal coil.Two scan protocols with different resolutions were used to scan the labeled cells. The images of SPIO-labeled cells were compared with that of the unlabeled ones. Results:SPIO-labeled pancreatic islet cells were seen on MR GRE T2~*W images as dark spots,and were more clearly seen on higher resolution images.Conclusion: SPIO-labeled pancreatic islet cells could be seen on MR GRE T2~*W images in vitro, and it helps to validate the feasibility of in vivo imaging.PartⅡStudy of labeling pancreatic islet cells with superparamagnetic iron oxide (SPIO) and tracking labeled cells using MRI in vivoObjective:To track SPIO-labeled cells in rats using MRI,and detect the survival and rejection of grafts after transplantation.Methods:15 male Wistar rats were used for study.SPIO-labeled cells were tracked using a GE 3.0T Signa Excite MR scanner equipped with an animal coil.(1) The images of SPIO-labeled cells in rats after transplantation were compared with that of the unlabeled ones.(2) FSE T2W sequence and GRE T2~*W sequence were used to scan the SPIO-labeled cells,and the sensitivity of images was compared with each other.(3) SPIO-labeled pancreatic islet cells isolated from Wistar and Lewis rats were transplanted into Wistar rats,and the survived islet cells were counted sequentially.(4) The rats of the syngeneic group were sacrificed three months after transplantation,while the rats of the allogeneic group were sacrificed three weeks after transplantation.MR images were compared with the pathological results.Results:(1) SPIO-labeled pancreatic islet cells were seen on MR images as distinct hypointense spots distributed in the liver of the rats homogeneously.(2) GRE T2~*W images were more sensitive to detect SPIO than FSE T2W images.(3) The relative count of hypointense spots in the syngeneic group was 90.03±9.52%,92.87±18.21%and 86.25±24.81%respectively one week, two weeks and three weeks after transplantation,while the relative count in the allogeneic group was 41.40±15.41%,33.41±14.01%and 23.58±16.78%respectively. The difference between them was statistically significant(P＜0.01).(4) Iron particles were detected only in the SPIO-labeled cells.The grafts were found well-preserved in the liver of the rats of the syngeneic group three months after transplantation,while only few grafts were found in that of the allogeneic group three weeks after transplantation.Conclusion:MRI could be used to track SPIO-labeled islet cells in vivo,and has great value to detect the survival and rejection of grafts after transplantation in rats.