3D ³¹P MR spectroscopic imaging of the human brain at 3 T with a ³¹P receive array: An assessment of ¹H decoupling, T₁ relaxation times, ¹H‐³¹P nuclear Overhauser effects and NAD⁺

Abstract

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 volume5 1 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.

Cerebral phosphoester signals measured by 31P magnetic resonance spectroscopy at 3 and 7 Tesla

“…In addition to potential contamination by MP, other factors may also affect metabolite quantification by 31 P MRS. For example, nuclear Overhauser enhancement is not uniform across the 31 P signals [ 41 ]; specifically, in contrast to the nearly uniform T 1 of most metabolites detected by proton MRS [ 42 ], there is a large dispersion in T 1 s of 31 P MRS signals [ 33 , 43 ], making their intensities sensitive to the commonly used TR values. Such variations may also have contributed to the different quantification results reported in the 31 P MRS literature.…”

Metabolic changes in the cingulate gyrus, precuneus, and white matter in anorexia nervosa using multivoxel MR spectroscopy

“…The values recorded corresponded to the areas under the peaks, assessed with the Siemens Syngo software (Siemens Healthcare) (Figures 2 and 3 ). 9 , 10 Processing was performed without user interaction and consisted of the following steps: Gaussian apodization (400 ms), spectral shift correction, sixth‐order polynomial baseline correction, and zero‐order phase correction. Curve fitting with Gaussian lineshape included NAA (main peak at 2.01 ppm and five other resonances between 2.46 and 2.84 ppm), Cr (3.02 ppm), Cho (3.21 ppm), mI (3.56 ppm), Cr2 (3.91 ppm), Lac (1.33 ppm), lip13 (1.23 ppm), and MM09 (0.9 ppm).…”

NAD+ metabolism: pathophysiologic mechanisms and therapeutic potential

“…It provides new approach to investigate intracellular NAD + redox state and metabolism in the human tissues with the potential for translation to human application. 654,[675][676][677][678] Isotope-tracer methods Isotope labeling metabolites, including [2,4,5,6-2 H] NAM, [U- 13 C] Trp, [U-13 C] NA, and NR (nicotinamide 7-13 C, ribose 2-2 H), can be intravenous infused into mice or added into the media of cell culture. The labeled metabolites in cells, serum and tissues are analyzed by LC-MS. Isotope-tracer methods are applied in quantitative analysis of NAD + synthesis-breakdown fluxes, including NAD + synthesis and consumption fluxes in cell lines, as well as NAD + fluxes in vivo.…”