In vivo brain 31P‐MRS: measuring the phospholipid resonances at 4 Tesla from small voxels

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Abstract
An optimized phosphorous (31P) three‐dimensional chemical‐shift imaging (3D‐CSI) protocol was developed at 4 T to study the phospholipid metabolism from discrete regions in the human brain without the need for 1H‐decoupling or nuclear Overhauser enhancement (NOE). In this study, a spherically bound, weighted average, random point omission 3D‐CSI technique was developed and tested, based on methods proposed in the literature. The technique yields a significant (p < 0.001, two‐tailed, 5% confidence level) increase in signal‐to‐noise (SNR) efficiency over conventional 3D‐CSI (phantom 32%), without an increase in voxel bleedthrough. An automated time‐domain fitting procedure utilizing prior spectral knowledge quantified the individual brain phospholipid metabolites from 15 cm3 effective (8.0 cm3 nominal) volumes from the left/right‐parieto‐occipital cortex and left/right thalamus in 10 normal volunteers. Individual constituents from the phosphomonoester (PME) region; phosphoethanolamine (PEth), phosphocholine (PCh) and the phosphodiester (PDE) region; glycerophosphoethanolamine (GPEth), glycerophosphocholine (GPCh) and membrane phospholipids (MP) were separately quantified to assess the precision of our method at 4 T against previous 1H‐decoupled 31P‐MRS brain studies at lower fields and much larger voxels. Derived concentrations (mM/l tissue) for PEth, PCh, GPEth, GPCh and MP in the left‐parieto‐occipital cortex were 0.81 ± 0.21, 0.46 ± 0.14, 0.74 ± 0.30, 1.15 ± 0.43 and 1.54 ± 0.95 mM, respectively, and 0.94 ± 0.16, 0.46 ± 0.17, 0.83 ± 0.22, 1.14 ± 0.40 and 1.26 ± 0.78 mM for the right parieto‐occipital cortex. Derived concentrations (mM/l tissue) for PEth, PCh, GPEth, GPCh and MP in the left‐thalamus were 0.69 ± 0.18, 0.42 ± 0.16, 0.63 ± 0.20, 1.05 ± 0.42 and 0.93 ± 0.56 mM, respectively, and 0.68 ± 0.24, 0.34 ± 0.18, 0.60 ± 0.23, 1.09 ± 0.36 and 0.74 ± 0.48 mM for the right‐thalamus. This is the first study to our knowledge that has been able to quantify each of these individual phospholipid metabolites from such small voxels in the brain within a clinically reasonable scan time and without 1H‐decoupling or NOE. Copyright © 2002 John Wiley & Sons, Ltd.

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