Modular 31 31 P wideband inversion transfer for integrative analysis of adenosine triphosphate metabolism, T 1 1 relaxation and molecular dynamics in skeletal muscle at 7T

摘要

Purpose For efficient and integrative analysis of de novo adenosine triphosphate (ATP) synthesis, creatine‐kinase–mediated ATP synthesis, T 1 relaxation time, and ATP molecular motion dynamics in human skeletal muscle at rest. Methods Four inversion‐transfer modules differing in center inversion frequency were combined to generate amplified magnetization transfer (MT) effects in targeted MT pathways, including Pi ? γ‐ATP, PCr ? γ‐ATP, and 31 P γ(α)ATP ? 31 P βATP . MT effects from both forward and reverse exchange kinetic pathways were acquired to reduce potential bias and confounding factors in integrated data analysis. Results Kinetic data collected using 4 wideband inversion modules (8 minutes each) yielded the forward exchange rate constants, k PCr →γ ATP = 0.31 ± 0.05 s –1 and k Pi →γ ATP = 0.064 ± 0.012 s –1 , and the reverse exchange rate constants, k γATP→Pi = 0.034 ± 0.006 s –1 and k γATP→PCr = 1.37 ± 0.22 s –1 , respectively. The cross‐relaxation rate constant, σ γ(α) ? βATP was –0.20 ± 0.03 s –1 , corresponding to ATP rotational correlation time τ c of 0.8 ± 0.1 × 10 –7 seconds. The intrinsic T 1 relaxation times were Pi (9.2 ± 1.4 seconds), PCr (6.2 ± 0.4 seconds), γ‐ATP (1.8 ± 0.1 seconds), α‐ATP (1.4 ± 0.1 seconds), and β‐ATP (1.1 ± 0.1 seconds). Muscle ATP T 1 values were found to be significantly longer than those previously measured in the brain using a similar method. Conclusion A combination of multiple inversion transfer modules provides a comprehensive and integrated analysis of ATP metabolism and molecular motion dynamics. This relatively fast technique could be potentially useful for studying metabolic disorders in skeletal muscle.