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Band inversion amplifies 31 P– 31 P nuclear overhauser effects: Relaxation mechanism and dynamic behavior of ATP in the human brain by 31 P MRS at 7 T
Author(s) -
Ren Jimin,
Sherry A. Dean,
Malloy Craig R.
Publication year - 2017
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26236
Subject(s) - nuclear magnetic resonance , relaxation (psychology) , chemistry , nuclear overhauser effect , magnetization transfer , adenosine triphosphate , human brain , spin–lattice relaxation , magnetization , anisotropy , biophysics , nuclear magnetic resonance spectroscopy , physics , magnetic resonance imaging , magnetic field , biochemistry , biology , nuclear quadrupole resonance , medicine , neuroscience , radiology , quantum mechanics
Purpose To develop an improved method to measure the 31 P nuclear Overhauser effect (NOE) for evaluation of adenosine triphosphate (ATP) dynamics in terms of correlation time (τ c ), and contribution of dipole‐dipole (DD) and chemical shift anisotropy (CSA) mechanisms to T 1 relaxation of ATP in human brain. Methods The NOE of ATP in human brain was evaluated by monitoring changes in magnetization in the β‐ATP signal following a band inversion of all downfield 31 P resonances. The magnetization changes observed were analyzed using the Bloch‐McConnell‐Solomon formulation to evaluate the relaxation and motion dynamic parameters that describe interactions of ATP with cellular solids in human brain tissue. Results The maximal transient NOE, observed as a reduction in the β‐ATP signal, was 24 ± 2% upon band inversion of γ‐ and α‐ATP, which is 2–3‐fold higher than achievable by frequency‐selective inversion of either γ‐ or α‐ATP. The rate of 31 P– 31 P cross relaxation (0.21 ± 0.02 s −1 ) led to a τ c value of (9.1 ± 0.8) × 10 −8 s for ATP in human brain. The T 1 relaxation of β‐ATP is dominated by CSA over the DD mechanism (60%: 40%). Conclusions The band inversion method proved effective in amplifying 31 P NOE, and thus facilitating ATP τ c and relaxation measurements. This technique renders ATP a potentially useful reporter molecule for cellular environments. Magn Reson Med 77:1409–1418, 2017. © 2016 International Society for Magnetic Resonance in Medicine