Global brain metabolic quantification with whole‐head proton MRS at 3 T. (5th July 2017)

• Record Type: Journal Article
• Authors: Kirov, Ivan I.; Wu, William E.; Soher, Brian J.; Davitz, Matthew S.; Huang, Jeffrey H.; Babb, James S.; Lazar, Mariana; Fatterpekar, Girish; Gonen, Oded
• Is Part Of: NMR in biomedicine. Volume 30:Number 10(2017:Oct.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-07-05
• Subjects: choline -- creatine -- diffuse brain disorders -- N‐acetyl‐aspartate -- normal brain -- proton MRS -- whole‐head MRS; Nuclear magnetic resonance -- Periodicals; Magnetic Resonance Spectroscopy -- Periodicals; 574
• DOI: 10.1002/nbm.3754
• Languages: English
• ISSNs: 0952-3480

Abstract

Abstract : Total N ‐acetyl‐aspartate + N ‐acetyl‐aspartate–glutamate (NAA), total creatine (Cr) and total choline (Cho) proton MRS ( 1 H–MRS) signals are often used as surrogate markers in diffuse neurological pathologies, but spatial coverage of this methodology is limited to 1%–65% of the brain. Here we wish to demonstrate that non‐localized, whole‐head (WH) 1 H–MRS captures just the brain's contribution to the Cho and Cr signals, ignoring all other compartments. Towards this end, 27 young healthy adults (18 men, 9 women), 29.9 ± 8.5 years old, were recruited and underwent T 1 ‐weighted MRI for tissue segmentation, non‐localizing, approximately 3 min WH 1 H–MRS ( T E / T R / T I = 5/101 /940 ms) and 30 min 1 H–MR spectroscopic imaging (MRSI) ( T E /T R = 35/2100 ms) in a 360 cm 3 volume of interest (VOI) at the brain's center. The VOI absolute NAA, Cr and Cho concentrations, 7.7 ± 0.5, 5.5 ± 0.4 and 1.3 ± 0.2 mM, were all within 10% of the WH: 8.6 ± 1.1, 6.0 ± 1.0 and 1.3 ± 0.2 mM. The mean NAA/Cr and NAA/Cho ratios in the WH were only slightly higher than the "brain‐only" VOI: 1.5 versus 1.4 (7%) and 6.6 versus 5.9 (11%); Cho/Cr were not different. The brain/WH volume ratio was 0.31 ± 0.03 (brain ≈ 30% of WH volume). Air‐tissue susceptibility‐driven local magnetic field changes going from the brain outwards showed sharp gradients of more than 100 Hz/cm (1 ppm/cm), explaining the skull's Cr and Cho signal losses through resonance shifts, line broadening and destructive interference. The similarity of non‐localized WH and localized VOI NAA, Cr and Cho concentrations and their ratios suggests that their signals originate predominantly from the brain. Therefore, the fast, comprehensive WH‐ 1 H‐MRS method may facilitate quantification of these metabolites, which are common surrogate markers in neurological disorders. Abstract : Our goals are to demonstrate that: (i) non‐localizing WH 1 H–MRS captures NAA, Cr and Cho signals exclusively from the brain in a quick, high‐SNR acquisition; and (ii) the Cr and Cho signals from all other head tissue compartments are lost to skull air‐tissue susceptibility gradients. Towards this end we quantified the NAA, Cho and Cr of the WH and of a 0.4 L brain‐only VOI. The two methods' similar NAA, Cr and Cho concentrations and their ratios to NAA suggests that the source of all metabolites' 1 H–MRS signals is the brain. Therefore, the WH approach allows global brain coverage assessment not only of NAA, but also of Cr and Cho, with a sub‐3 min acquisition at 3 T with high, over 500, SNR, enhancing the usefulness of the methodology for monitoring diffuse neurological disorders.