Assessment of tissue-engineered islet graft viability by fluorine magnetic resonance spectroscopy

T.M. Suszynski¹, E.S. Avgoustiniatos¹, S.A. Stein¹, E.J. Falde¹, B.E. Hammer², K.K. Papas^1
1 University of Minnesota, Department of Surgery, Minneapolis, MN, USA; ² University of Minnesota, Department of Radiology, Minneapolis, MN, USA

Objective: To evaluate whether fluorine magnetic resonance spectroscopy (¹⁹F-MRS) can be used to assess tissue-engineered islet graft viability by non-invasively measuring pO₂ and estimating islet oxygen consumption rate (OCR).

Methods: Scaffolds composed of porcine plasma were seeded with human islets and perfluorodecalin and each gel was covered with the similar volumes of culture media in Petri dishes (Figure 1).

Figure 1: Schematic of tissue-engineered scaffold.

Four different scaffolds were seeded with varying numbers (0-8000) of islet equivalents (IE), aliquoted from the same islet preparation. Run order was randomized and scaffolds were examined by¹⁹F-MRS at 37°C using a 5T spectrometer and a single-loop surface coil placed underneath each scaffold. A standard inversion recovery sequence was used to obtain a characteristic¹⁹F spin-lattice relaxation time (T1), which was converted to a steady-state average pO₂ estimate using a previously determined linear calibration (pO₂ (mm Hg) = 5.26·10⁵/T1 (ms) – 122; R² = 0.985). Each condition was assessed in replicate (n = 6-8).

Results: Scaffolds exhibited an IE dose-dependent increase in T1 and decrease in pO₂ estimates (Table 1).

From the difference between pO₂ estimates and ambient pO₂ (ΔpO₂), we calculated the islet preparation OCR to be 93 ± 10 (mean ± SEM) nmol/(min∙mg DNA) using theoretical modeling. This value compares well with OCR values measured with established methods for human islet preparations.

Conclusions:¹⁹F-MRS can be used for the non-invasive pre- and possibly post-transplant assessment of tissue-engineered islet graft viability by estimating the amount of viable, oxygen-consuming tissue remaining in a scaffold.