3D 31 P MR spectroscopic imaging of the human brain at 3 T with a 31 P receive array: An assessment of 1 H decoupling, T 1 relaxation times, 1 H‐ 31 P nuclear Overhauser effects and NAD +

31 P MR spectroscopic imaging (MRSI) is a versatile technique to study phospholipid precursors and energy metabolism in the healthy and diseased human brain. However, mainly due to its low sensitivity, 31 P MRSI is currently limited to research purposes. To obtain 3D 31 P MRSI spectra with improved signal‐to‐noise ratio on clinical 3 T MR systems, we used a coil combination consisting of a dual‐tuned birdcage transmit coil and a 31 P eight‐channel phased‐array receive insert. To further increase resolution and sensitivity we applied WALTZ4 1 H decoupling and continuous wave nuclear Overhauser effect (NOE) enhancement and acquired high‐quality MRSI spectra with nominal voxel volumes of ~ 17.6 cm 3 (effective voxel volume ~ 51 cm 3 ) in a clinically relevant measurement time of ~ 13 minutes, without exceeding SAR limits. Steady‐state NOE enhancements ranged from 15 ± 9% (γ‐ATP) and 33 ± 3% (phosphocreatine) to 48 ± 11% (phosphoethanolamine). Because of these improvements, we resolved and detected all 31 P signals of metabolites that have also been reported for ultrahigh field strengths, including resonances for NAD + , NADH and extracellular inorganic phosphate. T 1 times of extracellular inorganic phosphate were longer than for intracellular inorganic phosphate (3.8 ± 1.4s vs 1.8 ± 0.65 seconds). A comparison of measured T 1 relaxation times and NOE enhancements at 3 T with published values between 1.5 and 9.4 T indicates that T 1 relaxation of 31 P metabolite spins in the human brain is dominated by dipolar relaxation for this field strength range. Even although intrinsic sensitivity is higher at ultrahigh fields, we demonstrate that at a clinical field strength of 3 T, similar 31 P MRSI information content can be obtained using a sophisticated coil design combined with 1 H decoupling and NOE enhancement.