In vivo proton T₁ relaxation times of mouse myocardial metabolites at 9.4 T

Purpose Proton magnetic resonance spectroscopy (¹H-MRS) for quantitative in vivo assessment of mouse myocardial metabolism requires accurate acquisition timing to minimize motion artifacts and corrections for T₁-dependent partial saturation effects. In this study, mouse myocardial water and metabolite T₁ relaxation time constants were quantified. Methods Cardiac-triggered and respiratory-gated PRESS-localized ¹H-MRS was employed at 9.4 T to acquire signal from a 4-μL voxel in the septum of healthy mice (n=10) while maintaining a steady state of magnetization using dummy scans during respiratory gates. Signal stability was assessed via standard deviations (SD) of zero-order phases and amplitudes of water spectra. Saturation-recovery experiments were performed to determine T₁ values. Results Phase SD did not vary for different repetition times (TR), and was 13.1°±4.5°. Maximal amplitude SD was 14.2%±5.1% at TR=500 ms. Myocardial T₁ values (mean±SD) were quantified for water (1.71±0.25 s), taurine (2.18±0.62 s), trimethylamine from choline-containing compounds and carnitine (1.67±0.25 s), creatine-methyl (1.34±0.19 s), triglyceride-methylene (0.60±0.15 s), and triglyceride-methyl (0.90±0.17 s) protons. Conclusion This work provides in vivo quantifications of proton T₁ values for mouse myocardial water and metabolites at 9.4 T. Magn Reson Med 73:2069-2074, 2015.