Minimization of spectral pattern changes during HRMAS experiments at 37 degrees celsius by prior focused microwave irradiation

Object

High-resolution magic angle spinning (HRMAS) magnetic resonance spectroscopy provides detailed metabolomic information from intact tissue. However, long acquisition times and high rotation speed may lead to time-dependent spectral pattern changes, which may affect proper interpretation of results. We report a strategy to minimize those changes, even at physiological recording temperature.

Materials and methods

Glioblastoma (Gbm) tumours were induced in 12 mice by stereotactic injection of GL261 cells. Animals were sacrificed and tumours were removed and stored in liquid N₂. Half of the samples were exposed to focused microwave (FMW) irradiation prior to HRMAS while the other half was not. Time-course experiments (374?min at 37°C, 9.4T, 3,000?Hz spinning rate) were carried out to monitor spectral pattern changes. Differences were assessed with Unianova test while post-HRMAS histopathology analysis was performed to assess tissue integrity.

Results

Significant changes (up to 1.7 fold) were observed in samples without FMW irradiation in several spectral regions e.g. mobile lipids/lactate (0.90–1.30?ppm), acetate (1.90?ppm), N-acetyl aspartate (2.00?ppm), and Choline-containing compounds (3.19–3.25?ppm). No significant changes in the spectral pattern of FMW-irradiated samples were recorded.

Conclusion

We describe here a successful strategy to minimize spectral pattern changes in mouse Gbm samples using a FMW irradiation system.