Positive contrast visualization of SPIO-labeled pancreatic islets using echo-dephased steady-state free precession

Objective: MRI has recently been introduced as a promising method of monitoring the transplanted pancreatic islets labelled with superparamagnetic iron oxide (SPIO). However, the traditional {\hbox{T}}-2 -weighted approach frequently yields ambiguous results because of the negative contrast of the SPIO particles on the background of other body components. This obstacle could be overcome with the use of a novel method known as echo-dephased steady state free precession (SSFP), generating positive contrast in the presence of paramagnetic material. Methods: In phantoms, we achieved exact localisation and clear positive contrast visualisation of human SPIO labelled islets. Using the proposed method we demonstrated the ability to detect even a single pancreatic islet against a homogeneous background. Results: In vivo experiments in rats confirmed reliable and accurate localisation of transplanted SPIO labelled islets. Conclusion: The echo-dephased SSFP technique could successfully visualise SPIO-labelled human and rat pancreatic islets yielding a positive contrast.