Tracking Intrahepatically Transplanted Islets Labeled With Feridex-polyethyleneimine Complex Using a Clinical 3.0-t Magnetic Resonance Imaging Scanner

To evaluate the images acquired with a clinical 3.0-T magnetic resonance imaging machine as the quantification of transplanted and surviving islets in vivo. Polyethyleneimine (PEI) was introduced to increase the labeling efficiency of Feridex, a dextran-coated superparamagnetic iron oxide. Allogeneic (Lewis-to-Wistar) and syngeneic (Wistar-to-Wistar) intraheptatic islet transplantations were performed to study the relationship among magnetic resonance imaging, metabolic monitoring, and pathological examination. After receiving Feridex-PEI-labeled islets, dark voids could be observed in the livers of both groups, accompanied with a significant decrease in liver/muscle intensity ratio from 1.25 ± 0.03 to 1.09 ± 0.05 (P < 0.01). One week after transplantation, islet grafts were rejected in the allogeneic group. Rapid disappearance of dark voids and a significant increase of liver/muscle ratio were observed. No islet grafts could be found in the paraffin sections of livers by that time. Meanwhile, in the syngeneic group, islet grafts survived indefinitely. Dark voids persisted and low liver/muscle ratios retained. The fact that the dark voids represented the labeled islets was confirmed by combined staining of insulin activity and Prussian blue. Either spot counting or signal intensity measurement provides a perfect quantification of transplanted and surviving islets in vivo. Feridex-PEI provides an effective and safe way to label islets.