A comparison of cardiac 31 P MRS at 1.5 and 3 T

31 P MRS was evaluated on normal volunteers at 1.5 and 3 T, and the signal‐to‐noise ratio (SNR) of the two field strengths was calculated. The in vivo spin‐lattice, T 1 , relaxation times for PCr and γ ‐ATP, which are essential for correcting for the effects of radiofrequency saturation on the PCr/ATP ratio, were determined at 3 T. The T 1 values for six volunteers were 3.8 ± 0.7 s for PCr (mean ± SD) and 2.4 ± 1.1 s for γ ‐ATP, which are similar to reported values at 1.5 T, allowing us to use protocols developed at 1.5 T at the new clinical field strength of 3 T. Direct comparison between 1.5 T and 3 T in the same 10 subjects, using coils of identical geometry and identical pulse sequences gave a mean SNR for PCr at 3 T which was 206 ± 94% of that at 1.5 T. The linewidth for PCr increased from 13 ± 6 Hz at 1.5 T to 22 ± 12 Hz at 3 T. The coefficient of variation in the measurement of PCr/ATP, based on the Cramer–Rao lower bounds, was reduced from 32 ± 25% at 1.5 T to 18 ± 13% at 3 T. Thus, 31 P MRS at 3 T is greatly improved by the increase in SNR compared with acquisitions at 1.5 T because of the higher field strength. Copyright © 2008 John Wiley & Sons, Ltd.