Band inversion amplifies 31P-31P nuclear overhauser effects: Relaxation mechanism and dynamic behavior of ATP in the human brain by 31P MRS at 7 T

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Abstract

Purpose: To develop an improved method to measure the 31P nuclear Overhauser effect (NOE) for evaluation of adenosine triphosphate (ATP) dynamics in terms of correlation time (τc), and contribution of dipole-dipole (DD) and chemical shift anisotropy (CSA) mechanisms to T1 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 31P 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 31P-31P cross relaxation (0.21±0.02 s-1) led to a τc value of (9.1±0.8) × 10-8 s for ATP in human brain. The T1 relaxation of β-ATP is dominated by CSA over the DD mechanism (60%: 40%). Conclusions: The band inversion method proved effective in amplifying 31P NOE, and thus facilitating ATP τc and relaxation measurements. This technique renders ATP a potentially useful reporter molecule for cellular environments.

Original languageEnglish (US)
JournalMagnetic Resonance in Medicine
DOIs
StateAccepted/In press - 2016

Keywords

  • ATP
  • Cross relaxation
  • Dynamics
  • Inversion transfer
  • Magnetization transfer
  • NOE
  • T1 relaxation

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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