Determination of oxygen r₁ at 3 Tesla using samples with a concentration range of dissolved oxygen

Abstract

Objective

To investigate the sensitivity of modified Look–Locker inversion recovery (MOLLI) to measure changes in dissolved oxygen (DO) concentrations in water samples and to calculate sequence-specific relaxivity (r_1m) and limit of detection (LOD).

Materials and methods

Ten water samples with a range of DO concentrations were scanned at 3 T using two variations of MOLLI schemes. Using linear regression the r₁ of DO was estimated from the measured DO concentrations and T₁ relaxation rates (R₁). The results were combined with previously reported values on in vivo stability measures of the MOLLI sequences and used to estimate a LOD.

Results

DO concentrations ranged from 0.5 to 21.6 mg L⁻¹. A linear correlation between DO and R₁ was obtained with both MOLLI sequences, with an average correlation coefficient (R²) 0.9 and an average estimated r₁ ($\hat{r}_{1}$) of 4.45 × 10⁻³ s⁻¹ mg⁻¹ L. Estimated LOD was ≈ 10 mg L⁻¹.

Conclusion

MOLLI T₁-mapping sequences may be used for detecting dissolved oxygen in vivo at 3 T with an $\hat{r}_{1}$ in the range 4.18–4.8 × 10⁻³ s⁻¹ mg⁻¹ L and a corresponding LOD for dissolved oxygen of approximately 10 mg L⁻¹. MOLLI-based T₁ mapping may be a useful non-invasive tool for quantification of in vivo changes of DO concentration during oxygen challenges.