Abstract
Cardiac phosphorus magnetic resonance spectroscopy (MRS) with surface coils promises better quantification at 3 Tesla (T) from improved signal‐to‐noise ratios and spectral resolution compared with 1.5T. However, Bloch equation and field analyses at 3T show that for efficient quantitative MRS protocols using small‐angle adiabatic (BIR4/BIRP) pulses the excitation‐field is limited by radiofrequency (RF) power requirements and power deposition. When BIR4/BIRP pulse duration is increased to reduce power levels, T2‐decay can introduce flip‐angle dependent errors in the steady‐state magnetization, causing errors in saturation corrections for metabolite quantification and in T1s measured by varying the flip‐angle. A new dual‐repetition‐time (2TR) T1 method using frequency‐sign‐cycled adiabatic‐half‐passage pulses is introduced to alleviate power requirements, and avoid the problem related to T2 relaxation during the RF pulse. The 2TR method is validated against inversion‐recovery in phantoms using a practical transmit/receive coil set designed for phosphorus MRS of the heart at depths of 9–10 cm with 4 kW of pulse power. The T1s of phosphocreatine (PCr) and adenosine triphosphate (γ‐ATP) in the calf‐muscle (n = 9) at 3T are 6.8 ± 0.3 s and 5.4 ± 0.6 s, respectively. For heart (n = 10) the values are 5.8 ± 0.5 s (PCr) and 3.1 ± 0.6 s (γ‐ATP). The 2TR protocol measurements agreed with those obtained by conventional methods to within 10%. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.